Scrolling of windows

[John]

I have an oddity that is causing local problems

I have a collection of GNU/Linux computers all running he same version
(OpenSuse Leap 15.2) and all running the same emacs built from master
sources.  My main machine (X) allows one to put the mouse on the
scroll bar and holding the left button to scroll smoothly up and down.
The same is the case on machine C, but on machine T the scroll bar
jumps when the button is released but does not move until the release.

All three computers are 64bit; C and T are AMD processors of
different generations, and X is an Intel i7.  The only differences I
can think of is that C and X have been updated from earlier
distributions but T is a new computer installed ab initio.
All three run without a desktop system, with fvwm window manager.  No
KDE or Gnome used.

This behaviour seems only to be in emacs and other programs are
consistent (browsers, xterm mainly).

Can you suggest were I should look?  Or where I should ask?

==John ffitch