Unicode error in Plone resourceditor

I have a CSS file with:

.plone-has-table:after {
  content: "⟷";
  position: fixed;
  color: #cccccc;
  margin-top: -3px;
  }

The line comes
If I try to edit the theme TTW, it will not save due to 'unicode' errors.
Is this a bug or not.

I noticed that (theme) future imperfect has changes the same to:

 "\27F7";

Obviously a bug.
Traceback?

The unicode errors comes from the resource-editor javascript.
Will check when I am back...
Failed to load resource: the server responded with a status of 500 (Internal Server Error)

And when I click on it:

{
"error_type": "UnicodeDecodeError"

}

The error log shows:

Traceback (innermost last):
  Module ZPublisher.Publish, line 138, in publish
  Module ZPublisher.mapply, line 77, in mapply
  Module ZPublisher.Publish, line 48, in call_object
  Module plone.resourceeditor.browser, line 583, in __call__
  Module plone.resourceeditor.browser, line 533, in do_action
  Module plone.resourceeditor.browser, line 226, in saveFile
UnicodeDecodeError: 'ascii' codec can't decode byte 0xce in position 3673: ordinal not in range(128)

Looking at the change-log I see that this is supposed to have been fixed in version 3.0. I think I had some other problems when using 3.0 on 5.1.5, maybe I could try to downgrade to 2.1.1

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