Overload at 95%

[braquio]

Here the results of my tests (forgetting last issue):

From graveyard paying alternative cost:
Cyclonic Rift + Snapcaster Mage(with flashback spell previous played with overload) 100%
Cyclonic Rift + Snapcaster Mage(with flashback spell previous played without overload) 100%
Cyclonic Rift + Snapcaster Mage(both cases) + Twincast 100%

From hand for free cost:
Weapon Surge + Oracle of Bones 100%

From opponent hand for free:
Electrickery + Mindclawn Shaman 100%
(you can choose Electrickery with shaman but you cant play it if there is no valid targets so its ok)

Weapon Surge + Mindclawn Shaman 100%

From exile for free:
Electrickery + Isochron Scepter 100%
Weapon Surge + Isochron Scepter 100%

OTHER ZONES PAYING ITS NORMAL CASTING COST:
From exile:
Nivix, Aerie of the Firemind PARTIAL ONLY NORMAL PLAY 100%

From library:
Future Sight PARTIAL ONLY NORMAL PLAY 100%

I didnt test these cases:
From library for free (I don't have any of these cards: Knowledge Exploitation, Galvanoth, Spellshift)
From graveyard paying its normal casting cost (I don't have Bösium Strip)

CONCLUSION:
All seems work perfectly except of course the known limitation with other zones at its normal cost.

[NeoAnderson]

I am glad you think so. About the bug i think as like you is better to put a note to inform the users. Also because is a remote possibility caused by a no-sense action. We could suggest to play with "Automatic Resolution" option enabled.

[RiiakShiNal]

But if I have understand you suggest to modify the spell who is going to copy the card.
For example : Increasing Vengeance, Reverberate, Twincast should be adapted to store the card they are copying just before they make the copy...
If you mean this i already know but it means to modify a lot of standard cards and i want to stay far from do it.).
Also because there also many possible interaction who can cause weird behaviours (Counterspell, instant effects who replace others...)

No, you do have to modify the cards that do the copying, but all they would do is increase a global value by 1 for each copy they produce. They don't store pointers or do anything else. Only the card you would want to be copy aware would check that global and trigger on SPELL_PLAYED doing whatever it wants to the copy.