I just thoroughly re-read the IRS letter.  It says, "We reviewed your account and found that misapplied payment(s) totalling $3,015 (the amount owed).  We have adjusted your account to correct this error, and as a result you have a balance due of $3,015."  

That sounds more like the bank refused the draft.  I've asked the client to call the bank and ask tomorrow.

Thank you for your thoughtful questions tonight