Version:            (using Devel)
OS:                Linux
Installed from:    Compiled sources

I'm working with Plasma::Meter on kde 4.2 rc1, but I noticed this since some time.

Put a Plasma::Meter in a Plasma::Applet and set the size of the meter to, e.g QSize(4,178). The meter will put a margin of 1 pixel on the left and on the right of the bar.
If you change the height to 6 the margins will be 2 pixels large, and increasing the height will increase the margin itself, so, e.g. setting the height to 25 will make 6 wide margins. 
But try to set the height 5 pixels high: the margin will be 18!
And 5 is not the only one: 15 "returns" 10, 16 "returns" 2.

So, if in principle the margin increases with the height, there are some height values that break this "rule".