Reloading or closing page after editing causes data loss

[leoluk]

In Sync Mode, editing a page and then immediately closing or reloading it causes the change to be lost.

How to reproduce:

• Make a change.
• Press Ctrl-W or Ctrl-R immediately.

While there are pending unsaved changes, I suppose there should be a "Are you sure you want to leave?" prompt.

(I suppose it's related to #1040)