Can't PIE or Save: Editor gets into odd state when editing parameters.

I've seen this happen in other areas of the editor as well: Data Table fields (floats) for example.

Manually typing in numbers to fields seems less prone to this error; using spinners to drag values reproduces the error more reliably

Sometimes a restart of the editor fixes it.

Using attached project:
-Open project in Editor
-Open .../Content/UI/LoadingScreen_Widget
-Select "Loading" Image Widget
-From Details Panel ->Appearance ->Color and Opacity, click the swatch to open the Color Picker.
-Use Eyedropper to click light blue color of Border Widget
-Attempt to PIE

RESULT:
Warning is thrown: "Can't Play In Editor when performing Edit Color and Opacity operation"