Why does devd not capture stdout?

[Peter Steele]

I've created an autorun facility for USB drives using devd. I have the following addition in devd.conf: 

attach 10 { 
match "device-name" "umass0"; 
action "/usr/local/bin/autorun >/var/log/autorun.log 2>&1 &"; 
}; 

This works perfectly except only stderr messages appear in the autorun.log file; stdout messages are lost. If I run the same command manually: 

/usr/local/bin/autorun >/var/log/autorun.log 2>&1 

then stdout messages are captured in autorun.log as expected. 

What would cause this problem?