Sergey,
You are the man with the plan. Here is my question: We have literally a thousand customers and this bug only seems to affect 1 or 2 of them and it seems to occur on a fairly regular basis. Is it possible that there is something in their network setup that makes this more likely to occur? If so, do you have any idea what it might be? Again thank you!
A problem is a problem only as long as it has a possible solution. Lacking that, it becomes a FACT!