(I use Opera)

1. Open four Releases in four browser tabs
2. Click their four "Edit" buttons (that look like tabs) in the four browser tabs
3. Edit something (I did edit Artist Credit for instance) and click the "Edit Note" button (that looks like tabs) in the four browser tabs

There you go → « Internal Server Error » in the first three tabs and the last edit tab is OK, you can finalise it. For the three first edits, you shall do it all over again because it's in a strange status.

Here is the full error page :

Internal Server Error

Oops, something went wrong!
Error message: (No details about this error are available)
We're terribly sorry for this problem. Please wait a few minutes and repeat your request — the problem may go away.
If the problem persists, please report a bug and include any error message that is shown above.