It's something I've mentioned before but have been unable to reproduce and have doubted my own memory. However,  it seems it is a real issue though reproducing it is tricky. I went through the process of editing a project extensively and periodically saving and rendering and saving as an STL to check some measurements. I then went through parametrising the code and adding comments but didn't save the code, just rendered it and created an STL then closed without a save and it didn't warn me about the unsaved code and I lost all the latter changes. Fortunately because I did a render the backup was up to date :-) Sorry to say there is definitely a "hole" in there somewhere though it is very hard to reproduce. Regards, Dave