Why does VNAV set climb speed drop down to 250 knots

Despite setting TGT SPD in the CLB interface in the FMC to 293/0.78 (or MAX RATE or any other setting), when I engage VNAV speed drops down to 250 knots even after exceeding SPD REST of 250/10000. Any thoughts on why this is the case, and how to resolve it? I have reviewed the manual, and this is the quote:"TGT SPD: The Airspeed / Mach numberdisplayed at 2L represents that target climbspeed/mach number for the climb phase offlight. This is the target climb speed towhich the airplane will accelerate if operatedunder VNAV once the airplane is clear ofother, more restrictive speed constraints forflaps or regulated airspace."Of note, I am able to select VNAV, and it will control speed at 250 knots no matter what I set the TGT SPD to, and will therefore cause a very steep climb up to the ALT level I set in the MCP. I am getting no error messages, the plane just slows down to 250 even after exceeding FL10.Any ideas as to what I am setting incorrectly? Noel