Search Wizard not finding results - %5B%5D

I have used DataAssist Wizard to create a Search page and a Results page. One of the items (called Category) is a multiple selection list. The URL string passed to the Results page includes the %5B%5D coding for left and right bracket (see below) but this does not generate any search results.

If I manually edit the URL string to remove the %5B%5D then the correct results are displayed. I do want to have multiple selections for Category - can you explain what is going wrong please ?

?ItemType=Photograph&Category%5B%5D=Village&

I'll need to troubleshoot directly, see the private message section.

Jason, thanks for your help - the details are in the private section.

on the search page, i removed the [] brackets from the name.

i changed:
name="Category[]"

to:
name="Category"

the [] brackets are needed for a form that uses the post method with a multiple select list, but not for a form that uses the get method.