More odd conditions? Voiced obstruents as triggers and suppressors in Miri, Sarawak

Miri, an Austronesian language spoken in northern Sarawak, Malaysia, has two sets of vowel changes that are conditioned by voiced obstruents. In the first set, a last-syllable low vowel is fronted and raised to [e], or less commonly [i], if a voiced obstruent appears earlier in the word, while a penultimate low vowel immediately following the trigger is skipped. In the second, a high vowel in the final syllable undergoes breaking (diphthongisation) or lowering, depending upon specific conditions, unless there is a voiced obstruent anywhere earlier in the word. For both triggers and suppressors, this effect is cancelled by an intervening blocking consonant, which includes any nasal or voiceless obstruent except glottal stop. The challenge is to understand why voiced obstruents have this double function, acting as a trigger with low vowels and a suppressor with high vowels, given the lack of an a priori transparent relationship between low vowel fronting and high vowel breaking/lowering.