Here are two more screenshots:

#4a shows a text exactly as it was loaded from the file. The vowel
marks are totally missing, except for the word 'Allah', which for some
reason displays the vowel marks. The shaddah mark above that word, in
fact, is displayed twice, which is an error! You can see the word
'Allah' which is right at the left of the cursor. Those two marks
(shaped like the number 3, but rotated 180° degrees) above the word
are the shaddah. The reason for this anomaly might be that is some
systems the word Allah is a glyph on its own, which includes the
shaddah mark; if that was the case, this part of the problem could be
solved by removing any additional shaddah mark that might have been
added to that glyph. Anyhow, this was a digression.

The main problem is that the vowel marks are not displayed at all in
the other words.

#4b shows the same text, after the cursor has passed over them. This
is the nearest it comes to displaying the vowel marks correctly. But
again, they are out of synch with the letters, so the whole
vocalization is wrong!

Yet another two problems that I just noticed:
* the vertical space allotted to each line of text is not enough. You
can see from #4b that part of the vowel marks is cut off and thus
missing. This problem might be solved by increasing the inter-line
space, but wouldn't be nice if the proper inter-line space was
calculated and set automatically by the system?
* in #4b you can see, about 1cm at the left of the cursor, that two
vowel marks are overlapping in the same space, and of course they
shouldn't.