I had mine fitted by JSR 
… I think they bent the bulkhead bracket to take the strain off that clip you are talking about!
Even so, there were quite a few ‘mutterings’ my John during the install!!! 
Me too !!!
Make no mistake, it is a complete ****** to bend to shape, that’s why it may be done in a makeshift way
The TRD box was fitted by the dealer when the car was new , the filter was changed twice by the dealer and once by Sincs , nobody has said the box was fitted wrong , sounds like that could be the problem with the fit , I want it off anyway and change it for the VIS when Liam gets them in .
Have you got your intercooler on yet ?
I never bent the bracket on mine, I re drilled the support holes in the airbox to match the bracket, mine has never popped off 
Not even after a large curry!