Thanks. "Severity" is basically going to come down to the whims of the SRU team then.
To me, this is a deal-breaking regression, and I'm going to have to reinstall either 16.04 or 18.04 on that machine, because 19.04 will lose support before 20.04 is released.
To someone who doesn't use session restore though - which they probably don't, since Unity didn't even have it! - it's a trivial bug that doesn't matter at all.
I guess I'll just have to hope.
I skimmed the code quickly just now, and the actual save/load code is so simple that it's clearly correct. That's unfortunate, because it means the bug is either in meta_window_get_geometry when saving the session, or in an unrelated area after when loading it, and either way the regression is a side-effect of Something Else.
I can probably find and fix the actual bug fairly quickly myself, but I don't have the time to deal with the startup overhead of actually getting the thing to build - I've been down this road before with libraries etc we've used at work, and I know what a black hole for time it invariably is.
(And, jep - 30 minutes after cloning the repo, the typical issues with build systems requiring root and/or failing to acknowledge local paths for includes etc are as present as expected - but that's a topic for a different thread).
Thanks for answering the question as quickly and completely as you did: it's not the answer I particularly wanted to hear, but I was expecting that, and it's certainly not your fault.