Action: From the activities subpanel create a new email.
It works just fine. But if you have added a custom signature then creating a new email from activities panel gives you the following js error:
Error: Syntax error, unrecognized expression: <p>Best Regards,</p> <p>Helpdesk</p>
The unrecognized expression here is my custom email signature. As result the opened email popup window has no required fields populated.
When you cancel the email creation it looks like the jQuery has lost completely its focus and you need to relaod the Case.
This behaviour did not exist in the 7.10.12 release.
Workaround, do not use email signatures.