When selecting fields to show in Discover, the table reverts back to _source when clicking refresh (from the vis title)

Repro:

• Open discover
• Save a search (can be empty, you just need the title with the refresh icon)
• Select some fields to display from the sidebar
• Click the "refresh" icon next to the vis title
• Note how the only columns are time and _source

If you continue to mess around with columns and the refresh icon, you'll keep getting stranger results, as it's all out of sync.