Multiple spinners after cancelling Flow topic preview several times

In topic preview, if you click [Cancel] while the Cancel [Preview] [Add Topic] row is showing the animated spinner, the form and row of buttons go away (good). But if you bring up the form again by entering new text in the "Start a new topic" text field, the spinner reappears in the new row of buttons. Rinse and repeat for multi-spinner fun, see attachment.

The same probably happens if you cancel while the spinner is visible for other edit and preview actions for other Flow content. Because of bug 61169, I've been cancelling topic preview a lot.

Version: master
Severity: normal

Attached: