Updated to version 2.2+73-dev, text entry field disappears

I updated WYSIWYG from to version 2.2+63-dev to version 2.2+73-dev
I am using CKEditor 3.6.1.7072
The fields are Long Text fields, each using a Text Area widget.
I have two text formats defined that use the WYSIWYG/CKEditor: Full HTML and Full HTML-No Media.

Before the update, I could edit the contents of a Long Text field and change the text format without problems. Edits saved just fine.

After the update, I can edit the contents of the Long Text field and save without problems. If I change the text format to either of the WYSIWYG-enabled formats, the edit box with the text in it disappears, a blank space remains where the edit box should be, and the text format controls below the edit box remain visible. If I then refresh the page, the box reappears. This doesn't impact the capture of the edited text i.e. if I edit the text THEN change formats, then save, the edits are retained.

Further, once the edit box disappears, it does not reappear when switching to a text format that does not use WYSIWYG. It reappears only if I refresh the page.

I applied the patch from #1 here to v 2.2+73-dev: https://www.drupal.org/node/2427559, but it didn't impact the behavior.

Edit: this behavior is exhibited on two nearly identical sites.