This is new.
You all know me. I don't just walk in and go "hey, here's a problem I haven't googled into the ground". This one actually took me a solid 30 minutes to track down (and I found a bunch of PHP errors in the process so it was a good exercise anyway).
Ok this is search engine spider food:
When I select a service provider or service my site redirects back to the services page and doesn't select anything.
Hope someone found that on Google.
Now, go disable automatic-redirect creation in 404 redirected. It's eating the URL parameters.
You're welcome, future person that I don't know.