Steps to reproduce the issue

1 Go to article create and click the "Toggle Editor" button at tinymce editor to switch to source edit.
OR
1 Go to modules, new custom modul and click on the "Toggle Editor" button at tinymce editor to switch to source edit.

2 Type any text to the editor textare input and try saving the content in the blank texarea source mode.
3 The typed text is lost.

Note: These effects only at the blank textare mode without the tinymce toolbar, if in source editing mode.

Expected result

Text should be saved no matter in which editor mode

Actual result

Text is lost

System information (as much as possible)

Joomla! 4.0.0-beta1-dev Development [ Mañana ] 17-October-2019 20:21 GMT

Additional comments

Attached two screenshots to reproduce the issue