Will the behaviors of XFree86 be effected by different kernel?

[cckuo]

Dear X friends:
Recently I play the "rdesktop", a software like XP remote desktop, on
XFree86 4.3.0.
And the text will get blur only when I use Kernel 2.6.15.1 but it will
disappear when I change to kernel 2.4.27.
Since the accelerator in the XFree4.3.0 is XAA, are there some acceleration
in XAA will be effected by the kernel?
Ps: My platform is sis741. 
Appreciate your help in advance.
Sincerely Yours,
cckuo