On Mac OS, steps to reproduce:
1. Open a patch that uses some abstraction
2. Click on an instance of an abstraction to open it (or right-click, "open")
3. Change something in the abstraction and don't save.
4. Close the abstraction's window
5. Close Pd
Expected: the abstraction's window should open and the dialog saying "Discard changes in ...?" should be shown. You should be able to click on "Yes" to continue and close Pd
Observed: the abstraction's window does show up but the dialog is not shown. Pd waits for your answer but you cannot say either yes or not because the dialog with the button is not shown.
Maybe it's hidden somewhere and you may be able to force it to show up but I haven't found any way and I don't have much experience with Mac OS.
This does not happen 100% of the times, but quite often.
This means you cannot close Pd without saving changes (unless you kill it), which is pretty critical.
The issue has existed for years. I thought I had reported it but I can't find any bug report about it. I don't know if it's fixed in 0.43. It's 0.42.6 here.