I've seen this problem before. The problem I found was that the lower valve had some trash in it. The lower valve is behind the hydraulic bank on the left of the mast (looking at it fork on) (If you knew sorry). When I cleaned out the valve I found a little sliver of metal. I've also seen the return spring on the lower handle be too weak, and allow the handle to bounce. I know that typically the cylinder is a logical target, but have found the problem to be in the controls most of the time. Good Luck