Our use case:
A team consisting of several key account managers does have a common backlog.
Each key account manager ranks his items (e.g. by filtering against a certain filedAgainst-Category) on his own.
Then they sit together and agree on a team backlog ranking (over all filedAgainst-Categories of this team):
E.g. Story1 for Customer A has rank 1, Story2 for Customer B has rank 2, Story3 for Customer A has rank 3.

If the key account manager for Customer A changes the rank of his stories in his filtered view (Story3 before Story1), the teams backlog will show Story3 with rank 1, Story1 with rank 2 and Story2 with rank 3. So now both stories for Customer A are (unintendedly) ranked higher than those of Customer B.

Same behaviour when we try to use subteams for each customer: The ranking in the parent teams backlog when changing ranks in the subteam is affected in a way we cannot understand yet.