[CentOS] ipmi regression in 4.5?

I've been monitoring CPU temperature on a few Dell SC1435s running CentOS4
via OpenIPMI and 'ipmitool sdr'. It's been working very nicely, but the
upgrade to 4.5 not so long ago seems to have broken something:

  # ipmitool sdr type Temperature
  Temp             | 01h | ns  |  3.1 | Disabled
  Planar Temp      | 04h | ok  |  7.1 | 30 degrees C
  Temp Interface   | 53h | ns  |  7.1 | Disabled

The disabled sensors above used to work fine, and there have been no config
changes or bios upgrades or anything. All machines affected post 4.5.

Any suggestions?

Cheers,
Gavin