I ran about 500 rounds through my new XD40 and didn't like the heavy trigger pull so I took it to a local gunsmith and had the pull reduced to 4.5#.  Since then, about 2-3 times per 100 rounds, the trigger will just freeze until both the grip and trigger safeties are released and re-engaged.  I've taken it back to the smith and he can't find anything wrong with it.  I fabricated a couple of devices to engage both the grip and trigger safeties while shooting to eliminate the possibility that it was my grip or trigger technique that caused the problem but it still occurs.  Any ideas?

Your gunsmith fouled up your trigger job.  

Send it back to Springfield to have them do the trigger job.  You will have it back in 7-10 days with a trigger as smooth as glass.

They may even fix it under their lifetime warranty, but if you want them to lighten your trigger they charge a small fee to do the trigger job, and yes, they will do it right.

You may also want to ask the same question on www.xdtalk.com

That whole board is devoted to the XD.  

PS. I absolutely LOVE mine.

Quoted: Your gunsmith fouled up your trigger job.   Send it back to Springfield to have them do the trigger job.  You will have it back in 7-10 days with a trigger as smooth as glass. They may even fix it under their lifetime warranty, but if you want them to lighten your trigger they charge a small fee to do the trigger job, and yes, they will do it right.

+1