We have found the issue. This is due to RecordBrowsers 'enable_quick_new_records' option in the mail addon.
I do not recommend this, but if you need this urgently and you are comfortable with modifying the code, you can make a quick fix and comment line 290 in <you_epesi_dir>/modules/CRM/Mail/Mail_0.php so it looks like this:
// $rb->enable_quick_new_records();
We will work on this in the mean time and most likely release a new revision with a fix to this.
We apologize.