You shouldn't get the wrong idea that they are keeping done/undone just because they consider them more proper words for this context. A simpler reason would be that they are words far too embedded to be tracked down and removed. Changing them would probably break something. I believe WoltLab staff is aware that this unfortunate word choice has triggered some annoyance within WBB customers, and are probably planning to change them in a later release -- not likely 4.x.
This are two phrases for the same thing.
If you are referring to done/undone and resolved/unresolved I'm afraid you're mistaken. Undone doesn't mean that something is "not done" or not finished yet. Undone was widely used in the 18th century to define ruin and decay. Occasionally, its infinitive form to undo is used to express the action or intention to roll back to a former/previous state. Nowadays, Undone it's mostly avoided in colloquial English, and certainly it doesn't mean "unresolved" as you seem to claim.
This is mainly a support forum, and members usually start threads to ask questions that need answers, explain problems that need resolutions, and occasionally to chat about various topics. Logically, answered/unanswered and resolved/unresolved would still be better choices than done/undone.