We use some reports in SCSM (standard and custom). About week ago one of custom reports lost formatting when send to e-mail in MHTML format. We didn't modify this report before issue.
Report display correctly:
1. In the SCSM console.
2. In the SSRS web interface.
3. In the e-mail when format isn't MHTML (report is attached to message)
4. In any supported format (including MHTML) after manual export.
5. In any supported format (including MHTML) when report is sent to SMB share by subscription.
Report display incorrectly (as plain text without images and formats) only when it is sent in MHTML format by e-mail subscription.
SSRS 2012 SP1.