Hi Tim,
It is not expected to disappear. It might be caused by a browser extension I’m guessing (?), or the custom CSS is not printed (or cached),but I’m not sure.
I would recommend the following steps to perhaps get around it (it may sound strange, but usually works):
– Copy/Paste the custom CSS rule from the first point to the Custom CSS box again
– Do not save the options just yet
– Make a change to the pasted text in the input box, like adding a space after the last ‘}’ character – or simply delete one character and re-type it.
– Now save the options.
If this was related to any input validation issue, this might just do the trick.
Let me know!