This seems to be a WPF-specific issue.
If I set a breakpoint in the code, the program will pause when it reaches that line, and I can edit/add/remove code, and then continue - it runs the newly edited code (ie, it behaves as expected).
However, if I hit 'Break All', I get moved to window that says "Your App has entered a Break State...". If I try to edit my code, nothing happens. I try to type but nothing happens - no text appears, and there's no errors that pop up or anything.
I don't have this problem in WinForms applications - just WPF. If I create a basic WPF project from the template, I still have the issue.
It's a very frustrating issue! My ugly hacked solution is to add a button to my program's UI called 'Break', which executes a single line of code that has a breakpoint on it, basically recreating the behaviour that 'Break All' should have.
Weirdly, it's not an issue if I'm on a WPF project which uses multiple threads. Hitting 'Break All' in this case acts as if there's a breakpoint on the line of code where the background thread is set up.