Steps to replicate the issue (include links if applicable):

(this bug is specific to users with their username separated by a space/underscore)

• Appoint a user with an underscore separator in their name as an admin, e.g. Bennylin_(WMID)
• They cannot edit the contest page (button is greyed out) [Fig. 1]
• Remove the underscore (replace with a space), e.g. Bennylin (WMID), now they can edit the contest page [Fig. 2]

What happens?:
The contest editor page didn't like it when the username contain an underscore, even though in all wiki projects, underscore is treated the same as a space.

What should have happened instead?:
Make it work for the cases where one admin (A) add another admin (B) with an underscore on B's username by several methods

1. (easy) Replace underscores with spaces, when A adds B and click Save
2. (easy) Add a warning, when A try to add B which contain an underscore. A will need to make the adjustment before clicking Save.
3. (hard) Let A add B with underscore, and B could still edit the contest.

Software version (skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):