megaraid fails to probe SATA 300-8x

Starting with kernel 2.6.14-1.1637 and all subsequent kernels up through 2.6.16-1.2115 the megaraid module on my x86_64 system does not probe the LSI MegaRAID SATA 300-8x on boot.

The problem was introduced immediately after kernel 2.6.14-1.1532.

I originally suspected the problem implicated the megaraid module; I have become aware that even the same module version (megaraid
cmm: 2.20.2.6 and
megaraid 2.20.4.6) that probes and finds the LSI card in 2.6.14-1.1532 does not work later (specifically, 2.6.15-1830).

Thanks for any help in diagnosing what is going on.