*67 picks up 1st trunk from Pots trunks on GS 4108

Freepbx version 15 with Extension Routing.

10 Keysets
10 Pots lines on two Grandstream FXO Atas

The trunks are individual in the pbx and in the GS. Incoming calls route to each phone properly, when they try to dial out they go out the appropriate line. The problem is that when ANYONE dials *67 to block the caller id on the line the system grabs the first line on the first GS. If that line is in use the system returns with a All ckts busy message. The dial rule has *67 as a pattern. So the caller will get the line and then the line returns a tone to continue dialing and the call goes through. The CDR report shows the call utilizing the #1 trunk for the first ATA. Can someone tell me why this is happening?