Hi, I need some help regarding "d(b)d" and garbage dumps.

So I was looking at one of those "if you had one piece of advice to give to a newbie" threads, and someone posted about d(b)d. I tried it out, and it has been of an AMAZING help.

So now I have this garbage dump set up and it pretty much cleans out everything I ask it to. But...

Every now and then I will look in the dump, and find LOADS of Seeds and Spawn of all kinds, all marked as forbidden (like the actual junk), while my farmers are all screaming that they need more seeds.

Before anyone says "you just accidentally selected it when you went to dump things", I am absolutely positive that this is not so. In fact, even after they have stopped dumping, and I have irritatedly gone in and unforbidden all the seeds form the dump, and my dwarves take them out and start using them, I then go back later (without having used d(b)d in that space of time) and there are MORE seeds in there.

What is with this, and how do I fix it?

Thanks in advance.