Here is one of the XP2006 workshop antipatterns the group worked on.

Poor solution:
Not switching pairs

Forces:
High productivity of pair
Pair is happy
“never change a winning team”
Inability to pair with others

Consequences:
Pair does not improve
Pair will get bad habits (we always do it like this)
No knowledge sharing
Pair might get bored with each other
Needed split up impossible

Better solution:
Pairing schedule
Encourage pairs to switch

Exceptions:
Crisis
2 person team
Siamese twins