I'm a new rider this summer. I've noticed that many of the minor cracks in paved roads are repaired with (I assume) a bitumen type compound that is actually slippery. They are usually thin strips or lines filling cracks that have developed. I got a bit of a scare the first time I went over one as the front wheel seemed to slip/wobble. I had the feeling that if I hit or rode on a line of this stuff I could easily lose the bike from under me, especially if it was in a corner. Has anybody else experienced this or I am I being unnecessarily concerned?