The cause is with translations. The administrator did not intend for calls to phones with an active call to go to voicemail. See the following coverage path, used for their multiappearance stations:
display coverage path 4
COVERAGE PATH
Coverage Path Number: 4
Cvg Enabled for VDN Route-To Party? n Hunt after Coverage? n
Next Path Number: Linkage
COVERAGE CRITERIA
Station/Group Status Inside Call Outside Call
Active? y y
Busy? y y
Don't Answer? y y Number of Rings: 4
All? n n
DND/SAC/Goto Cover? y y
Holiday Coverage? n n
COVERAGE POINTS
Terminate to Coverage Pts. with Bridged Appearances? y
Point1: h99 Rng: Point2:
Point3: Point4:
Point5: Point6: