We are having the same problem.  We've asked several times, but, it appears that the consensus is it is a problem over here.  We cannot find the problem and the parts just continue to disappear!  I do not know how to fix this.  
You should also check to see if your Inventory Value and Inventory Listing both show that part number.  When I run both of these reports the parts in question show up on the Listing but not on the Value???  There are NO transactions done to these parts, nothing being Issued to WO's or adjusted out of stock, nothing...and the quantities just go away.  
 
 

We've emailed them several times, and they are now ignoring most of our emails.  I'm actually just the buyer over here and do not know much about this sort of thing.  I know enough that we are having some very serious problems.  I'm on here searching for people having the same issues and seeing what other people are saying to them.  Maybe this isn't the most productive way to find the fix, but, its all I can think of to do now.
 
Thank you for the information!
-Joanie