I've had this problem too. When planes do this, I have found that the flat part of the wing (between the two dihedrals) is at a slight anhedral (not sure if correct term; what I mean is angled down not up). It's very slight but if you bend that up I found it helps.Looking for an opinion...We've been playing around with different ideas, longer nose, larger wing (span), different wing position. Even mixing componants from different gliders. We have a glider now that has an absolute beatiful glide, slow, stable, reasonable sink rate, 3.5 grams. Great glide but when you launch it at more than 45 deg it will nose down and pile drive. It appears that when it is launched up and the climb speed terminates the wings have no lift yet, the nose rotates over at just about the CG ( slightly behind mid wing span). If high enough and there is time for the wing to develop lift and you get a great glide with whatever height you have left over. If launched at 45 deg or less (more less flat), again you get a beautiful glide but not much height. This model has the longer nose design. What does it take for a glider to nose over and begin gliding? Starting to see the dynamics but still missing something.
If that's not the case, sorry. Maybe making it more front heavy will help? I've also learned that sometimes a nice hand glide does not mean that it will launch/transition/glide down nicely.