Kerry, I agree that this is wrong and all PMs should have opportunity to weigh in about proposed merges.
It sounds to me like there is a logical (programming-wise, that is) reason for other PMs not to receive notification when a PM of the profile proposes the merge, though. The way the logic works, when a PM of one profiles proposes a merge of it with another profile then that is interpreted (by the software) as approval of the merge for that profile and it only needs approval from a PM of the other profile to complete. Thus, the proposed merge is automatically approved for the profile you manage, since it was proposed by another manager of the same profile. Now that it has been approved for that profile, there is no need to notify other PM's that their approval is needed, so you don't get email about the merge.
Disclaimer - I have no actual knowledge about this but am only speculating, based on my general knowledge of software logic.