Hi, X11 may not be the cause. As I reported, the problem occurs also in pure text mode, so it may just be the linux kernel or BootX. I remember updating to BootX 1.2.2 in the same timespan, as well as to kernel 2.2.17. The problem appeared with the frequency set to 63 (BootX setting). In the afternoon, with frequency set to 70, it was all OK. Please remember that I am using a PowerBook G3 1999.
Sergio