Message left in incorrect mailbox when using SMDI

I accidentally discovered a bug in my Asterisk voicemail system yesterday. I used two of my office phones (one PSTN and one VOIP) to call through our Plexus telephone switch to two different telephone numbers that have voicemail. The first call answered correctly and took a message. With only a couple seconds difference the second call’s SMDI info was never seen in the Asterisk console so the 2nd call left a message for the first call recipient.

If I included the applicable portion of my extensions.conf could someone tell me if there is something in I should change? I am wondering if the problem is indeed Asterisk or is in the switch.