Wildly incorrect framerate?

[ricks03]

Currently running CentOS-32 2.6.18-128.7.1.el5.centos.plus, ZM 1.24.2

I have three cameras hooked to the system using a LMBT44. All three are configured to capture 20 fps, and 30 when alarming. At that rate, everything seems to function nicely.

However, sometimes (it seems like when I'm updating the options?) the system goes nuts (CPU spikes, DASD takes off). When I look at /var/log/messages I see:

Sep 8 23:23:29 despair zma_m4[25405]: INF [Porch: 73000 - Processing at 166.67 fps]
Sep 8 23:23:29 despair zma_m1[25368]: WAR [Approaching buffer overrun, consider slowing capture, simplifying analysis or increasing ring buffer size]
over and over.

Now I know that the buffer overrun case is a problem, but I don't normally get this because the system is reporting somethign more reasonable:
Sep 5 21:07:44 despair zmc_dvideo1[10679]: INF [Porch: 7040000 - Capturing at 27.78 fps]
which is what I expect.

It seems like ZM decides that the framerate to capture is wildly too high, and then maxes the system out. But what's causing the erroneous framerate?

Thanks

rick