In Arabic shaping, I was told it's a strict requirement to join LAM and ALEF (and some combined variations) into a LAM/ALEF ligature.
Mlterm does this and appends following text directly to the ligature, for a seamless text flow.
Mintty also applies the glyph joining but leaves a space after it. While the result is ugly, it is consistent with the character-based locale-related width properties, which I think a terminal should maintain (also for emojis as handled by mintty).
There should be a statement about this in the recommendation, maybe even a switchable mode. The preference or default should be the locale-consistent behaviour, I think.