Sql Server 913 error: Could not find database ID

Strange behaviour of sql server I found.
When databaseid is changed in the sysdatabases, but name of database is same I get 913 error on some queries:
Could not find database ID %d. Database may not be activated yet or may be in transition.
It is totally thrue, my database have another id after series of drop/create, but somehow .NET SqlConnection remember it. There is no matter, if I am closing and reopen connection. I even did SqlConnection.ClearAllPools()
Even creating new connection with same connection string doesn't help. And it is not bug referencing by MSDN if I am using user-defined function. Nope, I don't have UDR in query.. But error appears in some specific queries, like Create mydb.dbo.mytable, or update, or insert..
One note.. I always use connection string with default database master
After drop/create database, I changed connection string and set default database name to the just created.

Bingo!!! It works!
But why?? Why connection of master, even with clearing pools, remember obsolete information from sysdatabases, if I even recreate new connection on it?
Didn't found any reasonable answer.