its actually quite simple. i updated my plugin to 1.13.1, and i soon found out that the Furnace object setBurnTime and setCookTime dont seem to have any effect.

they dont turn a furnace into a burning furnace, or turn a burning one back into a unlit one. getCookTime and getBurnTime do seem to function.. althrough, strangly, they do report the updated value, but the furnace in the world doesnt reflect the updates.