Enabling a disabled user and simultaneously changing password causes user lockout

To reproduce:

Edit a virtual domain FTP/Mailbox user and check the "Login temporarily disabled" box. Virtualmin correctly adds a '!' to the user's password hash in /etc/shadow. Returning and unchecking the box will also correctly remove the '!' from the hash, once again allowing the user to log in with their old password.

HOWEVER:

If instead of simply unchecking the box, you also use the "Set to..." radio button to simultaneously set a new password, the user's password hash gets prefaced with an extra "$1$!" and therefore does not allow any login at all. Subsequent attempts to change the password using Virtualmin all leave this extra string on the front, and a change by hand using the command line is necessary.