Before a syllable with a vowel sign above that has a narrow form, U+0F00 TIBETAN SYLLABLE OM does not behave like the sequence <U+0F68 U+0F7C U+0F7E> of which it is a duplicate encoding. I suggest substituting U+0F00 with that sequence in an early lookup.
Character data
ༀཀོ
U+0F00 TIBETAN SYLLABLE OM
U+0F40 TIBETAN LETTER KA
U+0F7C TIBETAN VOWEL SIGN O
ཨོཾཀོ
U+0F68 TIBETAN LETTER A
U+0F7C TIBETAN VOWEL SIGN O
U+0F7E TIBETAN SIGN RJES SU NGA RO
U+0F40 TIBETAN LETTER KA
U+0F7C TIBETAN VOWEL SIGN O
Font
NotoSerifTibetan-Regular.ttf
Where the font came from, and when
Site: https://github.com/googlei18n/noto-fonts/blob/85e78f831469323c85847e23f95026c894159135/hinted/NotoSerifTibetan-Regular.ttf Date: 2018-12-12
Font version
Version 2.000;GOOG;noto-source:20181019:f8f3770
Issue
Before a syllable with a vowel sign above that has a narrow form, U+0F00 TIBETAN SYLLABLE OM does not behave like the sequence <U+0F68 U+0F7C U+0F7E> of which it is a duplicate encoding. I suggest substituting U+0F00 with that sequence in an early lookup.
Character data
ༀཀོ U+0F00 TIBETAN SYLLABLE OM U+0F40 TIBETAN LETTER KA U+0F7C TIBETAN VOWEL SIGN O ཨོཾཀོ U+0F68 TIBETAN LETTER A U+0F7C TIBETAN VOWEL SIGN O U+0F7E TIBETAN SIGN RJES SU NGA RO U+0F40 TIBETAN LETTER KA U+0F7C TIBETAN VOWEL SIGN O
Screenshot