I have the same problem going into gravel strips.  There is a modification you can try to do to eliviate teh problem.  If CS will allow me to post this here, cause you have to edit teh aircraft config.

[contact_points]
static_pitch=-0.4
static_cg_height=17.3
max_number_of_points=14
point.0=1, 30.21, 0, -17.4, 1500 , 0, 1.46, 65, 0.2, 1.2, 0.7,  9, 8, 0, 250, 300

Just edit that 1500 value to another value.  The mains value is 2000, but I don't beleive they have the same "bouncing" problem.  Just play around with it.  Let me know what happens.

Brian