Just realized that I did not explain my setup clearly...
Using a vmware server, running latest FreeNAS, passthrough the M1215 to the FreeNAS, "supposedly" flashed in P15 version (purchased from ebay). At boot, it indicated BIOS version 6.14.05.2, FW package 24.2.1-0027. Quick google around, I find that driver/fw from broadcom all shows version 15.00.00.00 or 16.00.01.00, the 24.2.1-0027 seems to be a lenovo software version. Would this be a reason?
BTW, I blocked the B5/6 pin on the card based on a reading in this site to avoid the motherboard unable to boot issue.