Can't toggle `Flash LED on press` after removing a HA entity

[AKTheKnight]

Once I've selected (and then unselected) anything in the Entity field the "Flash LED on press" is greyed out and cannot be untoggled.

Steps to reproduce:

1. Select a button
2. Select any entity in the Entity field (See the Flash LED on press is now greyed out)
3. Delete everything in the Entity field
4. Oh no it's still greyed out!

This bug persists on that button if the config is then saved.

Config is attached:
localdeck-fce9fc.zip

It makes me almost want a "reset this button" button that I can use to wipe config for a specific button, instead of having to reset the entire config

[AAllport]

It makes me almost want a "reset this button" button

I will note this is a planned feature too