cd's not working when burned with k3b 'auto' setting

[fourhead]

i have a strange anoying cd burning problem with k3b. i have a samsung 52x burner and i'm using 52x cd's. i've told k3b my cd burner can do 52x and i've set k3b to auto-set the cd burning speed. ok, when i burn a 700mb file on a 700 mb cd, it starts burning at about 22x and continuosly speeds up to about 40x when the cd is about 70% full. after that, the cd burner speeds down (it's cleary hearable) in 2 or 3 steps, so that in the end, it would always stay at 40x for the last 30% of the cd. (i hope you know what i mean). cd burning quits with no errors. the thing is, when i try to read the cd, i can only read the first ~70%. exactly at the point where the cd burner has cut the speed down the cd is not readable anymore.

when i tell k3b manually to burn at 32x for example, it burns and reads the cd without any problems.

because the cd burner never goes about 40x, i guess the cd media can't do more. the problem seems to be that the speed is not continuosly slowly lowered, but in 2 or 3 steps. the cd media i'm using is a good one (tevion) and as i said it's supposed to do 52x. is there a way to tell k3b / cdrecord to stop doing that? i've already lost quite a few movies because cd burning was successful, but now i can't read them anymore. oh, when i watch a movie from the cd, as i said the movie stops at about 70%, but when i just forward the movie so that it starts playing after this 70% point then it can continue to read, so the problem really seems to be only this sudden-speed-down-point.

do you have any ideas on that or a similar problem?

tom