repro case:

1. create dashboard with two column 50/50 layout
2. add some panels into both columns
3. edit a panel in the right column, changing a property
   • reproduced with setting/changing/removing Limit on Query panels and adding a name for a new tab in a Tab panel without selecting a panel for it

expect: the change applied to the edited panel, layout remains the same

actual:

• change applied, but panel is now duplicated to the bottom of the left column
• survives refreshes
• can be moved around in the left column though the drag n drop experience is even more broken than usual
• can be moved to the right column. on refresh only one of them is rendered in the right column.
• deleting either of the instances removes both of them from the dashboard
• reproduced on multiple dashboards created from scratch
• reliably reproducible
• does not happen when editing panels in the left column

standalone instance

• libphutil b25e0477b280ca3e8345bb97cd55e95bcb5023ec
• phabricator dc2d87059b29b9dfe8838c2e0b07f4074f599112