Steps:

• enter this advanced query: assignee != "test.user"
• switch to simple editing
• click "View": jira searches for assignee == "test.user"
• expected: jira should display a warning that the JQL query is "too complex to display in the Issue Navigator edit controls." Or better yet, provide a mechanism to use NOT in the "simple" Issue navigator edit controls.

If I use another form of the NOT operator, for example: NOT assignee = "test.user"
Then jira correctly displays a "too complex" warning if I try to switch to "simple" editing.