Lao Sign Pali Virama and vowels above

[Richard Wordingham via Unicode]

When a consonant bears both U+0EBA LAO SIGN PALI VIRAMA (acting as a
nukta) and a vowel above, is there or is there intended to be any
constraint on there relative order?  While U+0EBA has canonical
combining class 9, the vowels above have canonical combining class 0,
so the order makes a difference.

Typographically, these marks don't interfere, but renderers may
consider that to be a problem. 

The example of nukta and vowel below has now gone up on Wiktionary at
https://en.wiktionary.org/wiki/ວິຍ຺ຍ຺ູ .  The rendering worry arises
with the other form of the instrumental plural masculine.

MS Edge is currently giving me dotted circles for the sequences
<U+0EBA, U+0EB8 LAO VOWEL SIGN U> and <U+0EBA, U+0EB9 LAO VOWEL SIGN
UU>.  I trust this is just a temporary aberration.

Richard.