André, what do you perceive as the "many advantages"?
“Many” might have been an overstatement — however, the main reason I want to like FontLab VI is the fact that it supports mark positioning and other opentype features which FontLab Studio can’t compile. IIRC it also will compile code which contains name strings for stylistic sets which would be much more convenient than having to insert them in DTL OTMaster. But try as I might I still much prefer working in FL5.
All of the problems which I’ve found with 5 in 10.13.13 appear to be clipboard related. You can make copies of outlines but you can't copy glyphs in the main window. It's also not possible to copy outlines to the mask layer which is a tad annoying.
I haven't found anything I need to do which can't be done, but certain operations become much more tedious. I’m hoping they’ll eventually fix this, though with FontLab VI already out I suspect it's not a high priority.
While FontLab VI offers many advantages over FontLab 5, I still much prefer the FL5 interface so I’m sticking with it for the time being.
Short answer: I’m not aware of a general workaround for the clipboard bug, but it’s still possible to use FL5 in spite of it. I should note though that I generally work with single masters. This bug might create problems for multiple master design that I am not aware of.