Summary:
In 7.3c when attaching a file to an email in the email editor the body of your email, including the 'To', 'Subject', 'CC, and 'BCC' fields, will be erased after the attachment is uploaded.


Symptoms:
Uploading an attachment in the email editor erases any email content that may have been entered.

Status:
This issue is resolved in 7.3c hotfix 1.