I made other changes to try to resolve the problem with layers but because I can't reproduce it, it is hard and I work in the dark.
Can you try RealCADD4.90b11 please?
I guess it simply must be something to do with the setup on my Mac, otherwise you would be able to replicate it. I really thought ditching eqmac2 had fixed it because for a while it all seemed OK, but then it started to happen again (which is in itself a bit odd - why was it OK for a while?) It's an irritant more than anything really and I've sort of got used to it! I suppose what I should do is completely clean out this mac, reformat the hard disk and start again – but that takes so much time I don't have!
The only difference between this mac and the standard is that I replaced the OEM 156GB SSD with a 240GB SSD from Transcend (their JetDrive 520) – I suppose there could be something in the configuration of that ... but that was a couple of years ago and this is (I think) more recent.
I will run Disk First Aid to see if there is something in the permissions etc. that needs fixing.