Good advice, highlandman.

I was once at a workshop conducted by a member of the Flanders Recorder Quartet. (check them out on YouTube) We tended to panic at the sight of 1/16th notes, to speed up, and to fall apart. The leader said he didn't know why people always do this, and he suspected it had something to do with Adam and Eve. An English speaker would have said "original sin."

I believe that's similar to what you've observed about some people speeding up in the hard parts.