How to reproduce

• I have a specific search model for contents of type "user" only
• The search criteria "content types" contains only the "user" content type and its subtypes

If I select "-All-" option for this content types search criterion, the results are contents of all types (article, news, ...)
It should be all contents of type "user" or its subtypes.

As a temporary fix, I had to set the content types search criterion mandatory