Same issue here - This happens to me very frequently and it is annoying. I am pretty sure this has something to do with clicking the spacebar while trying to do other commands during the block editing. I noticed the edit panel goes away the moment I press the spacebar.
As for the note to use the "unlock command". Once this has been implemented, every block created within my file is released from being a block.
I have also noticed that when working on a block item in a separate window, the command bar does not auto populate as you type. This can also being troubling for people who have difficulty spelling....(sad sigh).
TO ADD, I AM USING RHINO FOR MAC AND I JUST REALIZED THIS IS NOT THE RIGHT THREAD FOR THIS. MY APOLOGIES!!!