U+0F39 TIBETAN MARK TSA -PHRU gets a dotted circle after a vowel sign

U+0F39 TIBETAN MARK TSA -PHRU is in USE subclass CMAbv. U+0F71 TIBETAN VOWEL SIGN AA is overridden to Indic_Syllabic_Category=Nukta, so it is in subclass CMBlw. Other vowel signs are in subclasses VAbv and VBlw. Therefore, U+0F39 must precede all vowel signs. However, NFC reorders it after all vowel signs. Therefore, a normalized string like will get a dotted circle.

HarfBuzz handles this by normalizing U+0F39 to precede all vowel signs, but USE explicitly doesn’t support normalization, so how is USE supposed to handle this?

No file or test is named. Start by reproducing the U+0F40, U+0F71, U+0F39 sequence and reviewing the NFC ordering and USE subclass assignments described here, then compare HarfBuzz's handling. Done means the issue has a decided USE behavior for this sequence without relying on normalization.

Written by the indexing model from the issue text.