Strange hair patches when rendering

There is something wrong with the way Blender is rendering the hair. It’s happening on all of my previous files even, now! Not on just this character, but all of the other ones too.

Does anyone recognize the symptoms of this? ): Here is what the hair looked like before:

Now it looks like this:

It doesn’t even look like this in the 3D view, only render view.

Thank you!

EDIT: 1. I think I should’ve put this in the render section instead…
2. This render problem seems to only happen on Blender 2.65a, and not 2.64!

Got also a problem with hair : there could be something wrong with 2.65.
try to do a simple test :
With 2.64 with a cube, subdvide 1 face and make a vertex group, and apply particles hair for this VG only.
With 2.65 same test again (not use the precedent cube).
2.64 : ok - 2.65 : wrong
If you confirm, how to report the bug ?

I’ve seen that effect very recently when I’ve attempted to use Child Simplification on hair particles. However I’ve opened up Big Buck Bunny files (that use child simplification) and don’t see that effect. No resolution. Any ideas?