I had the same problem with my CLX450 and DUI hood when I first started diving dry.
I've found that my hood will always stay tucked in if I remember to put my hood on BEFORE I put on my BC. My theory is the BC shoulder straps press down on the warm-neck collar and hold the hood's skirt in place.
Once in a while I'll forget and put my BC on first, then do my best to tuck the hood into the collar ... it pops out about half the time.
I've found that my hood will always stay tucked in if I remember to put my hood on BEFORE I put on my BC. My theory is the BC shoulder straps press down on the warm-neck collar and hold the hood's skirt in place.
Once in a while I'll forget and put my BC on first, then do my best to tuck the hood into the collar ... it pops out about half the time.