Missing characters in Unicode (Devanagari)

I am working on tools for Indian Classical Music and they use the traditional Devanagari script.
The necessary fonts I have used on my system for years so they are correctly installed.

Within message boxes, comments, textedit objects or the like, some Devanagari characters are simply missing, or rather, hidden.
They exist int he textfields but can only be seen when the user edits it and are otherwise not visible.
The pattern seem to be:

• a word contains a diacritic character (such as ़ [nuqta]) or a ligature of two consonants is formed (by means of a ् [virama])
• usually the first character of all subsequent words will then be hidden (regardless of font or script), but sometimes other characters instead of the first

Does anyone have a clue on why this may happen and how to tackle it?

Monitoring the characters stream by means of atoi/itoa provides no clue as for all characters are passed through correctly, they simply don't display.

I have experienced similar bugs with different patterns in Excel before, so this may not be a Max-related Problem, but perhaps someone has an idea…

Thanks!