Had a problem in the past few days, once I minimized worms from frontend or the game it is impossible to restore it.
I know Husk has been having the same problems, after reinstalling everything found out that it works when you change the WA installation folder ex. from "/Team 17/Worms Armageddon" to "/Team 17/WA" for instance.
No idea why or how, but it seems to fix it (for now). You might want to ensure the "Restore associations on open" checkbox is ticked in Advanced Options so that you can still open wa:// links and the replay files are able to be open (right click wa.exe>run as admin only once for this to work). To clarify you do not always run the game in admin mode, you do this only once to restore associations.
Also I just seen camper mention this fix in another win 7 thread so i'm sure i'm not the first to figure this out but if you're having problems minimizing its worth a go.