When you import jar at the first time all is good, but when you make some changes and trying to re import your jar you realized that your old jar is stored somewhere and you can't delete it. I tried do this by hands, by synchronizing from local disk, by replication, nothing helps.
May be someone knows how to delete old jar and import the new one.
I know that when you rename new jar all is good. But I don't want to change version of my jar just because I don't know something about notes database.
Restart your HTTP task on Domino server after you changed a jar with server console command
restart task http
Otherwise the old version will still be used by JVM.
As an alternative you could add a version number to your jar like
my-classes-1.0.1.jar. Then Domino knows that the new jar has to be used.