When editing the "Advanced Options" for a synclist (under "Repo Management", in the "Remote" tab,) there's an option to enter a username and password. Entering and saving creds there works fine.

If later on you decide you want to remove that username and password, you'd like to be able to open up the advanced options, delete those items and then hit "Save". Currently that doesn't work - you remove them, hit save, and then the next time you open up the "Advanced Options" they appear as they did before.

Basically, once you have entered something into that field, there's no way to set it back to blank.