ChemDraw Beta 21.0 Portal
Example. Get the structure of cholesterol in the Chemdraw panel. In Chem3D minimise it, hide non polar H atoms and lone pairs. Structure 1
Copy it, paste it into a new file. In the Chemdraw panel mouse over C-12 and hit 'o' to change it into an oxygen atom. Minimise what you have and hide non polar H atoms and lone pairs. Structure 2. (this time it decided not to throw the conformation all over the place. Who knows why?)
Now copy both Structure 1 and Structure 2 into a third file and use the fast overlay to overlay them. Pick a bond in one of them and use the bond rotation dial to rotate just one bond in one molecule. (I cant grab an image of this as the tool disappears when I go to Snip and Sketch).
Crash. Picture 1. You may have to be a bit patient and do this with two or three bonds, but trust me, it wont take long for Chem3D to crash.
This has been a very consistent bug for some years now. Not limited to the example given. It happens with any overlay. It may take time, but it will happen.
Mike, I can confirm your observation and provide a video as an evidence (VD-CDBETA21-I-59.mp4). I believe, I can pin-point it to the default settings of "Use Back Buffer for Refresh" at:
File > "Preferences..." > OpenGL Settings > "Use Back Buffer for Refresh"
By default, it's On. If you turn it off, the described "cholesterol overlay" scenario doesn't lead to Chem3D crash. Would you, please, check at your testing PC, if you are getting the same behaviour for "Use Back Buffer for Refresh" Off? In my case all 3 Windows settings there are Off [turn it off, press "Apply", "Ok", close Chem3D, open and repeat "cholesterol overlay" scenario. Thank you.
picture added