HTML Area custom fields chaned by bulk update

Either this is a bug, or I am somehow doing something very weird.
If you have a Custom Field that is a “Edit HTML Area” on a ticket, and then do bulk update on that tiket, the content of the custom field is changed from whatever it was to “text/html”.
This happens when you don’t try to change the custom field i question.

Has anyone else seen this?
Present at RT 5.0.4 and RTIT 5.0.4

Best rgards