Invalid value passed for the allowInlineStyle option. The value must be a string.

[indigoxela]

That's what TinyMCE "whispers" into the console (no error).

So, this is a follow-up to a follow-up, to a... 🤦

Actually, this var shouldn't go to $options['backdrop'] but directly to $options as "backdrop" items get fed into tiny as additional editor variables (as strings). A bool is no string. 😜 And the info's only needed in the PreInit event handler, but no plugin needs it afterwards.

That does no harm, as the editor simply ignores the "wrong typed var", which it doesn't need, and shouldn't have got in the first place.