Trying to enter an url in the dialog to link a bug report to a merge keeps spinning

Go to a merge request, for example https://code.launchpad.net/~seb128/casper/+git/casper/+merge/409637 , click 'link bug report' and try to enter an URL as https://launchpad.net/bugs/1945831. The dialog gives a red label 'Please enter a valid bug number.' and a spinner that keeps rotating giving you no chance to correct your error unless you close the dialog and start again