I haven't tested this out in JK3 (I would think it is still there from JK2) but in JK2, servers force downloads of whatever .pk3 files that contain .jkb (bot personality) files *if* the server is using it at the time. Normally, the client doesn't start downloading it until the map changes but it still has to download none-the-less.

I think there should be some code change that makes it so that players do not have to download any additional .pk3 files due to .jkb files. I don't see why the client needs to have the .jkb file anyways, that's all info the server needs to know right?