DVD-Logic DVDtoBD subtitles issue

[Ghitulescu]

I have an issue with this software, I wonder whether someone else had it.
In short
I converted a commercially made DVD to BD, no editing or else, except for only two changes in DVDSubEdit for colours and position.
The bitmaps appear to be correctly done in DVDSubEdit, yet during the transcoding into BD sups, the very bottom line has been converted into a randomly coloured horizontally line. That happened in all subtitles.

Original VOB movie in VLC (cropped to the essential, also to save space):
http://forum.doom9.org/attachment.php?attachmentid=15675&stc=1&d=1482138290
The original subtitle (not cropped, full PAL resolution):
http://forum.doom9.org/attachment.php?attachmentid=15676&stc=1&d=1482138330
The original converted subtitle (not cropped)
http://forum.doom9.org/attachment.php?attachmentid=15677&stc=1&d=1482138384
And finally the same movie, now as M2TS, in VLC (cropped to essential, error pointed by an arrow):
http://forum.doom9.org/attachment.php?attachmentid=15678&stc=1&d=1482138441

Is there an explanation, some hints (what to avoid, although it's difficult to imagine what else more straightforward can be??)

[Ghitulescu]

I have to make some more tests, it appears that the random line appears at the position where the original bottom part of the subtitles was, before being raised in DVDSubEdit.

How this could happen is a mystery, since the raised up subtitle appears correctly in the extracted bitmap, see image #2 below. There are no "hidden" lines nor pixels ("hidden" as in a close colour, like FEFEFE instead of FFFFFF, not visible with the naked eye).
http://forum.doom9.org/attachment.php?attachmentid=15676&stc=1&d=1482138330