Assignment of "Main" Checkmark in Account Team

Hello community,

I am facing a strange behaviour when assigning the "Main" checkmark to members of the Account Team of an Account. It seems that there is a difference between certain party roles. The roles are the custom roles "Finance" and "Legal" with exactly the same settings in the Party Role Definition (see screenshot).

Still it is not possible to assign one account team member witth the role "Finance" as the sole main contact in the team, the system automatically checks another team member as "Main", when I try to do this setting.

But it is possible to do that with a member with the role "Legal", the system does no auto check of another member and seems to allow a "Legal" team member to be the sole main contact.

I wonder now, if there is a hidden logic behind it, or maybe it is just a bug, or maybe I'm missing something?

Hopefully someone out there knows a solution for this.

Thank you in advance!