It happened a number of times for me; clicking the help button in the window capplet, and yelp keeps respawning. It also happened to me when using the Help menuitem.
wow that's nasty, adding to blocker list.
Which applet is it exactly? Window Selector? Window List? All of 'em? Add which version of yelp do you see this with?
I see it with the yelp thats in rawhide currently, and it also happens when you start yelp from the commandline.
one thing to keep in mind is that we are not shipping the latest yelp currently, and upstream has moved from using bonobo-activation to using dbus, so it may be wise to wait for gecko 1.8, and check that the problem still occurs with the latest upstream, before diving deeply in this.
looks like the latest yelp works much better.