Minecraft Mouse Problem on Mac

You do not need to use both buttons; the function you describe is just left-click drag.

• Left-click dragging will split the held stack evenly across all slots dragged over. (If the destination already contains some of the item, then equal counts will be added to the existing counts, so the result will not be even.)
• Right-click dragging will put 1 item in each slot dragged over.

For whatever reason, OS X has a small amount of mouse latency. An application called SmoothMouse is supposed to fix it, although I haven't verified this.

There was a popular blog post by the author of SmoothMouse a few years ago which details the issue. John Carmack weighed in in the comments:

You can measure all this objectively. I took a few minutes, pulled out my handy high speed camera, and shot some quick video dragging a window around on my windows desktop and my old macbook. I used the same mouse, a Razer DeathAdder, on both systems.

Someone with more time should do a more exhaustive set of tests with a tripod and a trivial app instead of window dragging to make the data cleaner, but the results are so dramatically different that it isn’t a matter of splitting hairs.

Even being generous with exactly which frame the mouse started moving on, I never counted less than 10 frames (at 240 hz = 42 milliseconds) and sometimes as many as 17 from the time the mouse moved to the time the pixels on the screen started to change. I’m sure this is better on a more modern system.

The PC result was surprising. I was running on a 120hz monitor, and I couldn’t positively identify any frames of latency between the mouse starting to move and pixels on the screen changing. ...