• Create a user like "fred#1" and give them assign permission
• Create an issue and assign to this user
• Go to Issue Nav and construct a Basic search for assignee = fred#1
• Switch to Advanced Search, and click the search button

Expected:
Switch back to Basic
Actual:
You are not allowed to switch back to Basic

Furthermore, this user should have appeared in the "Suggested Users" section of the drop-down, but they do not.