I remember someone telling us the same thing before. Generally, renaming might be a good idea.

However, I can't come up with a suitable alternative. Unfortunately, the participial forms "finished" and "completed" are no names for actions. Using "finish" or "complete" (the corresponding proper action-verbs) seems odd, because you "close the task when it is finished/completed", you do not actually finish or complete it by executing the closing action.

Another thing I'd like to know. How easy is it, really, to confuse the word "close" with "close" like in "closing a dialogue", since -- from the top of my head -- we do not have actions like this in Kunagi at all.

All your points make sense. All I can say is that I pressed the button when I expected the "sub window" to contract a few times before I figured out what was going on.