List of steps to reproduce (step by step, including full links if applicable):

• Edit the Override list ("include-list") for an "all wikis" election through the interface (e.g. https://vote.wikimedia.org/wiki/Special:SecurePoll/votereligibility/1079/edit/include )
• Add a username without an @*wiki, implying a global username (e.g. Foobar)
• Save the page

What happens?:
The page takes a fairly long time to save (possibly looking for attached accounts for Foobar) and ultimately adds them all for each attached wiki, which can be many hundreds of entries.

By way of example, this is what it looks like to add Christian Humborg (WMDE): https://vote.wikimedia.org/w/index.php?title=SecurePoll:1079/list/include-list&diff=prev&oldid=1599

Also, adding other users to this list in the future appears to force the system to add more entries for those already on the list, such as here with Grzegorz Kopaczewski (WMPL) : https://vote.wikimedia.org/w/index.php?title=SecurePoll:1079/list/include-list&diff=next&oldid=1599

I worry that in the future, should this list become really long, this ceases to be efficient and may lead to timeouts and other problems.

What should have happened instead?:
The user should have been added as one entry, perhaps normalising to Foobar@global.