A funny thread between the 3h marker and the tip of a sort of secondary second hand is visible in IE 9 and IE 10. The same effect can be seen in IE 8 when using excanvas.js.
If the second hand is switched off, then this effect will affect the minute hand but only after it jumps to the next minute marker.
Another observation: when using a custom skin that does not have an outer border and no minute/hour markers, this effect is not visible.
The effect is visible with coolclock 2.1.4 and 3.0.0-pre.
Fixed by changing line 261 from
if (skin.outerBorder && !CoolClock.config.isIE)