HOW TO REPRODUCE:
Write a line that is quite wider than the screen. Go to
the end of the line. Now go to the left using the
'left' key (press it 15 times for example).
SciTE scrolls horizontally to the left while it was not
necessary, making it impossible to have the cursor at
the left of the screen while showing the end of a long
Also, once the SciTE starts scrolling, it continues to
scroll every time one press the left key (or
control-left or end) making the screen redraw many
times where it was not necessary.
It should stay in the same position unless you go to
the edge of the screen and need to scroll in order to
see what is under the cursor.