Call tree view in profiler: small bug

Hi,

The call tree view that's been added to the profiler in 4.4 is
wonderful!  One look at the tree gives you a good indication of
where your program is spending your time.  This is a lot better
than staring at the numbers in the cumulative view that we had
so far.

There's one minor bug though: when scrolling vertically (using
the scroll bar thumb) through a tree that doesn't fit in the window,
the percentages aren't always refreshed correctly.  Sometimes the
top half of those numbers seems to disappear.  This does not happen
with the function names, which are always displayed correctly.

(This is on LWW 4.4.5.)

Arthur