I suspect the issue with library lists manifests when multiple applications
are using the same connection pool to an individual host. Bad idea,
instead an application specific connection pool should be used.
I agree with Charles about the probable source of the problem. This is an application design concern - not necessarily a system administration or system configuration / tuning concern.
However, I would suggest that "library lists" generally have an association with "environments" such as "development", "test", "demo", "production". Or environments associated with hosting multiple database libraries for multiple customers. So your connection pool procedures need to take that into account. This can get pretty detailed, so what a lot of shops do is to set up separate LPARs for separate environments, rather than changing the designs of applications; that to me is not ideal. But LPARs let's lazy developers get away with kludges like hard coding library names in SQL statements.