I have had this exact problem with Poser 8 and Poser Pro 2010.

However, I didn't know that if I hit undo again, it would work.

I never report bugs because I've had negative experiences doing so in the past (though not with Poser support). I got tired of being told that every bug I reported was a problem with my machine, and concluded that reporting bugs was a waste of time for people like me. If a bug affects enough people, it will get reported by someone else, and if it doesn't affect very many, then it won't be high enough priority to be fixed.

ETA:

I ask about possible bugs in this forum because I want to know 1. if anyone else experiences them (because if not, then maybe it is a problem with my machine) 2. if anyone knows the cause (because sometimes there are specific triggers) 3. if anyone knows a work around.

I've never tried to contact SM, but I'm going to guess that reporting a bug that may not even be a bug to SM support is not necessarily going to get me a quick answer that will help me finish a render, whereas posting a question in this forum has definitely helped, and I've often got solutions with remarkable speed.

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PoserPro 2014, PS CS5.5 Ext, Nikon D300. Win 8, i7-4770 @ 3.4 GHz, AMD Radeon 8570, 12 GB RAM.