Submission page asks to "Reload page" when selecting a filter

When on an assignment submissions page, if you select one of the filters in the Options area, the page automatically reloads to apply the filter.

The behaviour seems to have changed somewhere between 3.9 and 4.0.

If you have changed nothing else on the page (i.e. not entered any other form value), the old behaviour would be simply that the page reloads.

It's now warning (tested in Chrome & Firefox) that "Changes may not be saved".

This must mean that some form element has changed, perhaps in javascript, after the page has loaded. This is likely to be annoying for avid users of the Filter options.