Mortar build freeze

Have you ever seen the mortar build just freeze at the end? like as if you where building it and suddenly ran out of pop cap. You can qua up other builds in the support barracks behind the mortar but nothing builds because the mortar is frozen.

This has happened to me twice now. I'm in a game, build a mortar, then later I start thinking where the hell is that mortar. I check the support barracks and its built to the end but wont come out. check my pop cap and its fine. No other mortars on the field.

It happened today, I canceled the mortar build, later tried a mortar build again and it built the second time and it wasn't pop cap because I checked that.

Did you upgrade mortar while producing it? It always cause block. Don't upgrade any unit while producing it.

humm, I guess thats possible, I didnt check that.