Bug when transliterating Unicode digraphs

I have been working on a project to develop a Sgaw Karen [ksw] to Thai [tha] language pair and as part of the project, I wanted to develop a transliterator between the three+ Sgaw Karen orthographies. Using https://user.keio.ac.jp/~kato/SgawKarenRomei.pdf as a guide, I developed a small test .dix, which I show below:
```

abcdefghijklmnopqrstuvwxyz ဖခဘ ံ ိ ၣ်

hpဖ

hkခ

bဘ

iံ

oိ

a

fၣ်

```
It seems to successfully compile as a .bin with `lt-comp`

```
lt-comp lr rom-test.dix rom-test.bin
consonants@inconditional 4 5
vowels@inconditional 3 5
```
and `lt-expand` shows the correct mapping:
```
lt-expand rom-test.dix
hp:ဖ
hk:ခ
b:ဘ
i:ံ
o:ိ
a:
f:ၣ်
```

However, when testing with `lt-proc -t` I get incorrect output:
```
printf 'hpi hpi\n' | lt-proc -t ./rom-test.bin
ဖi ဖi
```
(Expected output: ဖံ ဖံ)

It seems that none of the vowels will render after a consonant, but a vowel by itself or in succession will render just fine:
```
printf 'i i\n' | lt-proc -t ./rom-test.bin
ံ
```
To be sure, I ran the first prompt through `hexdump` and it confirmed that the 'i' is just passing through as-is. So it seems to be a compilation problem, not a unicode problem. (or is it a compilation problem stemming from a Unicode problem?)
``
printf 'hpi hpi\n' | lt-proc -t ./rom-test.bin | hexdump -C
00000000 e1 80 96 69 20 e1 80 96 69 0a |...i ...i.|
0000000a
```
**Update**
Interestingly, the vowels transliterate without issue if there is a space between them and the digraphs:
```
echo "hk i" | lt-proc -t rom-test.bin
ခ ံ
```
However, of course, the consonant and vowel need to be together (ခံ), which is not an issue with non-digraph inputs
```
echo "bi" | lt-proc -t rom-test.bin
ဘံ
```
Any help would be appreciated!