Bug - Fluxcharger and Onward // Victory

[tntsparkz]

When Fluxcharger is in play without summoning sickness, I cast any instant, which permits me to reverse Fluxcharger's power and toughness from 1/5 to 5/1. I allow this to resolve to an empty stack. Then, in my main phase again, I cast Onward from Onward // Victory. This triggers the game to ask if I wish to switch Fluxcharger's power and toughness again. I say no. I observe Fluxcharger still has a 5/1 power and toughness. The stack states Fluxcharger will get +5/+0. When the stack resolves, Fluxcharger ends as a 5/6. The result being that double strike does 10 damage instead of 20.

[Marek14]

This is not a bug. Basically, changes in power and toughness have several sublayers. And the very final sublayer is switching. The final state is: Fluxcharger is 1/5 -> gets +5/+0 to 6/5 -> power and toughness are switched to 5/6. And this will be the result regardless on when in the turn the switch happens.
If you decided to switch the values again, then the two switches would cancel out and you'd end up with 6/5 creature.

Comprehensive rules say:

613.4d Layer 7d: Effects that switch a creature’s power and toughness are applied. Such effects take the value of power and apply it to the creature’s toughness, and take the value of toughness and apply it to the creature’s power.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Its new power and toughness is 4/1. A new effect gives the creature +5/+0. Its “unswitched” power and toughness would be 6/4, so its actual power and toughness is 4/6.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Its new power and toughness is 4/1. If the +0/+1 effect ends before the switch effect ends, the creature becomes 3/1.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Then another effect switches its power and toughness again. The two switches essentially cancel each other, and the creature becomes 1/4.

[kanecharles]

This is not a bug. Basically, changes in power and toughness have several sublayers. And the very final sublayer is switching. The final state is: Fluxcharger is 1/5 -> gets +5/+0 to 6/5 -> power and toughness are switched to 5/6. And this will be the result regardless on when in the turn the switch happens.
If you decided to switch the values again, then the two switches would cancel out and you'd end up with 6/5 creature.

Comprehensive rules say:

613.4d Layer 7d: Effects that switch a creature’s power and toughness are applied. Such effects take the value of power and apply it to the creature’s toughness, and take the value of toughness and apply it to the creature’s power.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Its new power and toughness is 4/1. A new effect gives the creature +5/+0. Its “unswitched” power and toughness would be 6/4, so its actual power and toughness is 4/6.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Its new power and toughness is 4/1. If the +0/+1 effect ends before the switch effect ends, the creature becomes 3/1.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Then another effect switches its power and toughness again. The two switches essentially cancel each other, and the creature becomes 1/4.

wow very thorough explanation. I didn't know about these until reading this post. Thank you for sharing. By the way, when using an effect that changes a creature's strength and tenacity, if I then apply another effect that reverses the strength and tenacity, what will the end result be?

[Marek14]

This is not a bug. Basically, changes in power and toughness have several sublayers. And the very final sublayer is switching. The final state is: Fluxcharger is 1/5 -> gets +5/+0 to 6/5 -> power and toughness are switched to 5/6. And this will be the result regardless on when in the turn the switch happens.
If you decided to switch the values again, then the two switches would cancel out and you'd end up with 6/5 creature.

Comprehensive rules say:

613.4d Layer 7d: Effects that switch a creature’s power and toughness are applied. Such effects take the value of power and apply it to the creature’s toughness, and take the value of toughness and apply it to the creature’s power.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Its new power and toughness is 4/1. A new effect gives the creature +5/+0. Its “unswitched” power and toughness would be 6/4, so its actual power and toughness is 4/6.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Its new power and toughness is 4/1. If the +0/+1 effect ends before the switch effect ends, the creature becomes 3/1.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Then another effect switches its power and toughness again. The two switches essentially cancel each other, and the creature becomes 1/4.

wow very thorough explanation. I didn't know about these until reading this post. Thank you for sharing. By the way, when using an effect that changes a creature's strength and tenacity, if I then apply another effect that reverses the strength and tenacity, what will the end result be?

You always compute power and toughness without taking any switch effects into account. Then, if there is an odd number of switch effects, you exchange the numbers.