Sorry it's taken so long to get a response, Ambermonk.
This isn't a bug, but a design decision. The act of dragging a player into a slot on the substitution screen is the equivilent of having them announced in that slot.
There are really two things you can do:
1. Make sure of your choice before you drop them into the slot.
2. Make a thread in our Suggestions forum to request a change in the mechanics for the 2007 release.
I'm going to go ahead and close this. If you feel I've done so wrongly, feel free to shoot me a PM.
