yep, sounds like typical minecraft modder response... "it's not specifically our mod, so you're f*cked.".
at the same time, sounds like shitty programming practices/IDGAF, since for this bug to actually be an issue it sounds like they are relying on the framerate for timings. Rule 1 of game programming: don't lock shit to a user's hardware capabilities... of course vsync is going to delay GL calls to keep shit in sync with your refresh rate.