I've now installed the 32 bit Legacy version of Bodhi on an old IBM M50 as well. It has the same high CPU usage anomaly by terminology when running nmon. I upgraded the kernel to 4.10.0 so as to make Bodhi aware of the hyperthreading in the Pentium 4 CPU (w/ default non-pae kernel htop and nmon were only showing a single core in CPU meters; now show both threads). Thought such might by chance address the anomaly as well, but no terminology is still running high CPU when running nmon, even with new kernel.
The anomaly seems to only manifest when the terminology tab running nmon is the one brought into focus. If I start nmon in one terminology tab and then switch to a second terminology tab and check from htop the terminology CPU use drops off. Same if I check CPU use from a different virtual desktop/workspace than the one with terminology focused on running nmon.
Curiously, when I tried placing a small xfce4-terminal window over a maximized terminology window with nmon running in the terminology window and htop running in the xfce4-terminal window on top of it the CPU anomaly went away when the xfce4-terminal window running htop had focus ... even though terminology was actively displaying nmon output visibly in the background. When focus was brought back to the terminology window CPU use rose again.
Charles, did you test specifically the Legacy version in a 32 bit VM? As I've now reproduced the anomaly on two different 32 bit Pentium 4 machines (well, a P 4 and a P 4-M, one with hyperthreading and one without) I'm wondering if your test may not have been effectively emulating 'apples-to-apples'.