Yuck!

Now I'm not sure what these cups are called, but they are plastic and have a rubberized band that wraps around the cup for decoration.  Many of them are personalized.  Our were VeggieTales ones.

Recently, one developed a leak and I thought to cut and peel off the rubberized VeggieTales part to use for a future craft project.  I was disgusted to find that the cup and rubber parts met with glue and some unknown black substance that didn't look like anything you'd want your kids to come in contact with.

I rubbed some of it off with my finger and, thinking that hardened adhesive shouldn't rub off like that, quickly deposited both cup and rubber into the dishwasher to get sanitized.  I also peeled off the rubber from the cup that didn't leak.  Those both went into the dishwasher, too.

The dishwasher didn't get all the black off - I had to wash the pieces by hand to thoroughly clean them.

Now, the black stuff may just have been the color of the adhesive, but I'm not going to take any chances and let my kids use those type of cups again.

Has anyone else encountered such a thing?  Is the black gunk harmless?