Backgroundrb devel - Jul 2009 - successive asynchronous calls not happening

Hello,

I am running a job asynchronously three successive times in a loop  
with different parameters.  Only the first call happens, and the two  
other calls just get dropped.  If I sleep in between my async calls,  
all three occur.  All three calls work correctly, without sleep, on a  
different machine running Ubuntu.  I am running OS X 10.5.6 and am  
using memcache for my result storage, although not sure if that is  
relevant.  The calls I am making look like this:   
MiddleMan.worker(:master_worker).async_process_job(:arg =>  {:job  
=> :generate_static_map, :path => Route.static_image_path(id,  
preset), :width => width, :height => height, :data => self.data_full})

Any ideas? I''ve been tinkering around with this for a while and am  
coming up empty handed.

Thanks,
Zack