[xmonad] urxvt slow rendering

[Richard Watson]

Hello

I've been a long-time xmonad user (over 5 years) on all my machines, 
installing using the Debian package.

I'm currently running Debian jessie kernel 3.16 on my main desktop.

Recently I upgraded Debian on my primary desktop (jessie kernel 3.16). 
I'm running xmonad v0.11,  instead of v0.10 on my other machines.

I notice that when certain GUI application are running (e.g. Chrome, 
vmplayer, but not firefox & thunderbird) my urxvt terminal renders 
*really* slowly, redrawing the window line at a time! I also notice a 
huge X server CPU load (25-50%, as shown by top).

I've looked at X server logs and config and cannot see anything that is 
unusual.

Could there be an xmonad issue here? Has anyone else experienced 
something similar?  Any hints as to how to debug this?

--Richard Watson