I had the same problem to a smaller degree. As Houston recommended, I put a 3mm plastic spacer on the shock shaft to limit the amount of uptravel, problem solved! It doesn't really effect the overall dampering or working of the shock, just at that critical end point which usually isn't reached very much anyway. As long as you have plenty of droop (about 116mm) you'll be fine.
**Team Terribles Northern CA Regional Rep.**
Cold Fusion R/C Products Team Driver
Answer-RC USA / Team Sweep Racing USA
Team RcRenew...visit us at rcrenew.com!
Triton RC Alpha Plus Engines