cursor disappears and reappears on a regular basis

[Robert P. J. Day]

context:

  severn beta
  2.6.0-test4-bk1 kernel
  inspiron 8100 with external USB optical logitech mouse

starting only recently, when i'm in X, the cursor regularly vanishes,
only to reappear a few seconds later, usually at the edge of the screen.
strange behavior, and nothing i've ever seen before until recently with 
the really recent 2.6.0 test kernels.

thoughts?

rday