Does the Hudson filesystem SCM "Clear workspace" option work?

I am trying to use Hudson filesystem SCM to monitor an area, and kick of a build when it changes. It has been working fine with one area. I have just added a new job for nother area, and told it to "clear workspace". This seems to go into a spin开发者_如何学C - I've had builds queued up continuously, each claiming to have found 2396 new files. The documentation for the plugin suggests this sould be working, and I can't imaging why they would have provided the feature if this is not how I am supposed to use it, but any ideas what is wrong?

I think I have fixed it. It was polling every minute, but taking several minutes to fetch. I had expected that polling would be suspended while the build was under way, but it is not, so the next one along found lots of missing files in the frechly cleared folder. Setting the polling interval to

0,10,20,30,40,50 * * * *

seems to have fixed it.