CiviEvent DB Error when combining Individual sub-type and Participant custom fields

This is my first bug report so I hope this make sense and is done correctly. I'm also not sure if the priority is correct (its major for me but ...)

On Drupal6 CiviEvent throws "DB Error: constraint violation" when processing an Online Registration under the following circumstances:
1) a single event profile combines Individual sub-type fields and Participant fields; OR
2) an event has two profiles, where one profile includes Individual sub-type fields and the other includes Participant fields

If Individual sub-type type fields are not used the process works fine.
If Participant fields are not used then Individual sub type fields can be used

This was tested and replicated on drupal6.demo.civicrm.org.

The problem:

• Either lose valuable participant information by not using Participant fields in the event registration process
• Or avoid using the sub-type - but then the registration process overwrites and changes existing individuals' Contact Type (which will have to be fixed afterwards)