Also you have to consider some of the cards that the developers coded were only intended for use in certain specific challenges and as such they either hard-coded certain functionality or they only tested within the confines of where the card was used. One such example is
Cloudpost the card as it was coded by the developers only supports up to 6 loci on the battlefield because it was not intended for use by the player and there were no other loci that had been coded so without mods it is impossible for more than 6 to be on the battlefield at once. This "bug" can only be partially fixed as you would have to add a fairly large number of resource mana abilities to cover all contingencies (to be consistent with the rules, most people would simply cut it off after a reasonable number and limit it to that max). Then you have the bug below to worry about.
An example of a bug that we can't fix is wasted mana. For example the only untapped mana source available is
Sol Ring which produces

and in hand you have a
Basilisk Collar and
The Rack. Theoretically (and according to the rules) you can cast both, but due to how DotP controls mana tapping and usage you can only cast one.