Is pavement crack sealer dangerous?

I was out riding the other day on a road I hadn't been on in a while. One part of the road has a sharp curve combined with a shallow downhill. As I entered the curve at around 20 MPH, I discovered that the road had been painted almost edge-to-edge with a spiderweb of that rubbery tar-like stuff they use to cover cracks in the asphalt. Probably something similar to this stuff. Almost immediately I could feel my tires start to squirm around like they were about to skid. Thankfully I was able to stay in control, but, as I've had incidents like this several times over the years, I'm wondering if this stuff is really as slippery as it feels? Or does it just feel squirmy because it's made mostly of rubber so it kind of stretches a little, but won't let the wheel fully slip sideways?

After one particularly scary incident a few years ago on a really fast downhill, I usually try to avoid rolling over the stuff, but every so often I get caught off guard, like this time. So I'm wondering if anyone else has had problems with this stuff on the roads.