Not sure how I did this one, but I have two extensions, phantom #234 and desk phone #345.
I have a different phone #999 that has it's own mailbox, but nobody calls it.
#999's voicemail light is blinking for new messages, but it's not showing #999's voicemails. Intead it is giving notifications for both #234 and #345's voicemails (combining their total).
I had earlier tried to forward calls from #234 and #345 to #999 by adding #999 as an associated destination in dynamic extension express, and I believe that is related to this.