It's called roleplay. While I find myself in this position as well sometimes. a) most of the time it's pretty obvious what advances a conversation. b) always say what you WANT to say. Sometimes it might me more text/info sometimes advancement, but you do not "loose" anything except maybe a few minor backgroundinfos you do not need anyway.
No, it's called "unclear writing or interface". Sometimes it is clear, but many times it is NOT clear that an option will lock you out of all other options.
