Yeap!!!! Mulch harbors some weird looking stuff. That's were some of my "things" came from. About 10 years ago my DH had 2 big truck loads of mulch, really waste from a local pine wood processing plant, hauled into our yard. I moved mulch by the wheel barrow loads numbering in the high hundreds to every bed we had. And everywhere I put this stuff, I had a hard black crust settle into the beds. I spent hours digging it out and finally just resorted to using a long swing blade to chop the stuff up. Once is was broken up, it finally began to compost into the soil. That stuff was terrible. Not all free stuff is good stuff. It did work great on my paths and around shurbs but my perennial beds took a long time to recover. I didn't lose any daylilies that I had in the beds but it sure stunted them for a couple of years.
Now, I buy pine mulch by the bag fulls and it is working great! But, be it known, even pine mulch was had some of the weird things growing in it.
Boy, it's late and I'm really tired. Night folks!!!