I've noticed this happen in quite a few TT runs already but wasn't exactly sure what it was until I actually got into testing it a bit. Basically on bosses such as coredash, emperor, minister etc. that use ranged attacks which debuff your channelling speed, I've noticed my sage unfetter resists this debuff entirely if I time it right.
Though I'm aware it says on the skill itself it resists "disabling" debuffs the actual icon that shows up on your bar says "movement" debuffs. This also doesn't stack with vacuity powders and I've tested those too, they do the same thing.
Has this always been happening? I never heard of this before as (as far as I knew) channelling debuffs are not a movement debuff, and even if one would consider them as such if referring to "skill movement" it doesn't justify that silence doesn't get resisted, nor attack speed debuffs. I've tried asking other seekers on the server but most of them haven't actually tested that far or never even noticed it to begin with.
Edit: Tested it with a psy guildie just now. He cast Disturb Soul on me and the "Resist" popped up right above my head.