I noticed that ckVWM does this. Not intentially, but because it doesn't support dual monitor setup. I ran Simplicity like this for a while. I had to mess around with ckVWM features a bit because when I selected an application on the secondary monitor it switched the VWM to the primary monitor. A setup like this has it's appeals but over all I foudn it slightly too buggy to tollerate.

You may want to put your secondary monitor on the right of your primary monitor as most themes will display better this way.