The appearance of the flag dialog box after a custom flag was raised:
The custom flag box tells me "This is the flag you currently have raised". While this is technically correct, it isn't very useful because it doesn't tell me exactly what my flag contents were i.e. what exact message I had written for the moderators.
I have to look up the users/flag-summary
page, scroll down to the specific URL, and then see what my message was. This isn't a terribly bad problem, but I don't think it's really hard to include my custom flag text in the flag dialog itself. So, I think this can be considered for implementation.