If there is a brewing stand that is empty or contains only glass bottles, shift clicking a single glass bottle will stack them in the brewing stand. This can be repeated to get stacks of 64 glass bottles in each slot.

I believe this to be unintended as simply clicking and moving a stack or shift clicking a stack results in only one glass bottle being moved, so this seems to be a harmless yet unintended bug.

Stacking the bottles in this way seems to give accurate comparator outputs, and even more so, is able to produce all signal strengths 0-15 that a brewing stand otherwise wouldn't be able to. This could be considered useful in some redstone projects, though none specifically come to mind