IP Phones showing on 2 vlans

Hey all,

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I'm going down a rabbit hole looking for network issues in an environment, while looking for rogue switches I noticed some IP phones are showing up on both Vlan 1 and the voice vlan, but on some ports this is not happening. Example:

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StackSW01#sh mac add | i 2/0/44 1 0010.4940.178b DYNAMIC Gi2/0/44 1 3860.7783.3d92 DYNAMIC Gi2/0/44 200 0010.4940.178b DYNAMIC Gi2/0/44 StackSW01#sh mac add | i 2/0/47 1 1866.da1e.6d4b DYNAMIC Gi2/0/47 200 0010.493f.f715 DYNAMIC Gi2/0/47 

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Any idea what causes this?