I've talked to Adobe Customer Support several times about this and every time they can't fix it and tell me they will get back to me, but then a day or two later I get an email saying the support case is going to be closed. So, I'm wondering if this is an issue that can be duplicaed on any copy of Premiere Pro (at least on Windows). Watch my video and give it a try yourself. Let me know if you get the same result.
Also, before you ask, I have tried doing this with "Import Workspace From Projects" checked and unchecked. It still happens either way.
If it's a known issue, they haven't been telling their phone or chat tech support people. I called about it twice and both times they connected to my computer, tried a bunch of different stuff that didn't work, and then told me they'd have to call me back. Then I'd get an email a day or two later saying they were closing the case.
There are lots of bugs with workspaces since v15 that I've found. I can't get Premiere to remember stuff here and there but haven't pinpointed exact steps like you. It's absolutely buggy and for some reason isn't remembering certain things. The biggest problem I have found is that it doesn't remember "list" or "thumbnail" view in the project panel. Always resets to thumbnail view.