HTML not supprted in the scheduled emails?

HTML not supprted in the scheduled emails?

I tried both in my account in one of my clients' account, but I've got the same results.
I made a custom schedule - an email with attached xls reports. The problem is that the email is sent as plain text, and the html tags appear in plain text (<strong> , <br> and so on), even if content type is html . Is this a known problem in Scheduler?

Regards,
George