I think that freezing only makes mold go dormant. Its still there and would grow at a much slower rate, but once it gets some heat to it, it will start up again.
Just how long has the glop in qusetion been in there??!!??
Not all that long ... maybe 4 weeks or so. But I'm pretty sure it was put up during the rainy spell we had in mid-October, when several batches of leftover goo grew mold before we could get them in the freezer! I suspect this ... whatever it is ... was already infected (?) before it was frozen, and I just didn't see it.