I tested it in personal repository.
Create repository with named "test01 .html". Do two branches. Try create PR from first branch to second.
After select branch, click continue in create PR dialog.
Next step of create PR is unavailable(button create disabled).
Browser console contains exception:
GET https://bitbucket.base.url/rest/pr-harmony/1.0/users/~currentUserLogin/test01-.html 406 ()