Mine remains until I use it. I've had one ready to use and one waiting to be collected. Had this for several hours then used them fairly close to each other. Not sure why yours disappeared.
I don't think this has anything to do with a cheat. I think this is a problem with the game. Example, I get attacked and lose but still earn crowns. I earn crowns on every defense and I've done nothing to force that.
No. You cannot have two at a time; however, you can wait to use your first one until the second one is generated so that you can have two in back to back attacks (strategy for future alliance wars if incorporated).
Nothing is "automatic." Developers of games are far different than developers of commercial applications. You can only do so much to predict how the user base will jack with your application.
Allow me to clarify: I never disagreed with those who exploit bugs as being labelled a cheater. I just disagree with labeling everyone a cheater when some could simply be victims of a bug with no way to do anything about it.
You know, if all you talk about is the negative aspects then that is what you will most likely get out of the game. I'm enjoying this game and I couldn't care less about the less honorable.
Bulkhead designs are the best designs. You do have a version of it yet I don't think the TC should be a defended building. Wait until some version of alliance wars or until you are pushing for medals.