So I just checked it on my unit, using HX Edit 2.52 with Helix 2.54.
If I choose a dual cab, and I change some options on the first cab, then select the second cab and make some edits, then go back and select the first cab and change what it is, the second cab stays what it was originally at, and it keeps my edits.
If I choose the second cab and make some edits to it, the first cab is not affected.
What exactly are the steps you are making that are giving you frustrating results, and what is the result that is happening?
What does happen to me, and this is working as designed; When I select the new cab, it changes all the settings to the default setup of that cab, and if I go back to the original cab I was using there, all the changes I made are gone. But, as I noted, this is working as designed.
Man, I hope someday they allow us to create a library of settings for all blocks (IOW, give us a third column in the device column set that let's us see a list of user defined block setups).