I've create a private Codeforces mashup and would like to disable manager mode and submit solutions to the ongoing mashup as a contestant. I'm trying to click this button:

Instead of disabling manager mode as expected, Codeforces just refreshes the page, and I stay in manager mode. If it's helpful for debugging, here's a video of it happening.

If I'm using the tool incorrectly (or my account is in an invalid state or something), A) what am I doing wrong, and B) IMO, I think it would be helpful if CF displays an error message or something telling me what the problem is rather than just silently failing.