Well, everything is in the title. Crash happened right now after I opened a third script in about three minutes, using "edit script" in the contextual menu of the object to which the script is attached. This happened with 5.3, happens with 5.4 and now with 5.5. (On a side note, I'm a bit disappointed that the version of Mono Develop we use is the same as the one used with 5.4 and 5.3...) Edit: obviously, this doesn't happens each time, only from time to time... I don't know about the copy and paste problem yet.