scrollbar inconsisten behaviour (in run dialog)

I tried this with the windows dir of win98. When klicking in the scrollbar
itself (not on one of the buttons) it does:

a) scroll to that point
b) move 1 step (1 column) towards that point
c) move an arbirtrary number of steps (3 or 4) towards that point

when i click on the left or right button it more or less does the same, it either:

a) scrolls all the way
b) moves 1 step
c) moves an arbitrary number of steps