Just do it. Put some random crusaders you are never gonna use on it, if you succeed then it's great, if you fail then you don't lose anything. There is absolutely no reason to skip any mission, unless you have so few crusaders that you can't fill all mission slots (something that should only happen to very new players).

It doesn't matter, failing a mission has no consequences. I have about 1600 failed mission (and 52k successfull ones), because for the unimportant ones I don't even bother selecting the best crusaders. If a mission bothers you, instead of giving you the option to remove it (needing extra code from the devs) you can just run it. Worst case scenario, you lose nothing, and if you succeed, you get a speed boost.

How about another suggestion for a fix? Stop being so sensitive and whining about something that is easily ignored. So what if there's an unfinished mission on the list? Your OCD isn't the developer's responsibility.