I am extremely picky about my cursor movement. I use a mouse with one of the best current sensors (PMW3360). I have mouse acceleration totally turned off (via writing my own driver + careful tests).
I am quite
certain that my input device works as expected.
This is using macOS 10.12.4. I have tested with a number of input devices and cursor-controlling methods.
In this gif I am using the "Use pen/tablet-safe mode -- do not reposition mouse cursor while adjusting knobs/etc...".
I move my physical device (mouse) exactly 3" inside a wooden frame attached to the mousepad.
In the same frame, without clicking a control, the mouse moves exactly to the edge of the screen then back.
This is a difference of about 1700 pixels on my screen between the correct position and where Reaper sets the cursor.
Why does this matter?:
This behaviour (and the default without the option) make it so resetting the mouse/pen position after using a control must constantly happen.
Reaper's current behaviour does not allow the user to maintain physical device position in a 1:1 correlation to the cursor position, like nearly every other application's controls do.
Example 1 - Mouse: I click a pan control and move it to max left position. My cursor is now 100px to the left, but my physical device (mouse) is on the far right of the mousepad. Now I must lift the mouse, jiggle it around and reset the cursor->device locational parity.
Example 2 - Tablet in absolute mode: I click a pan control and move it to max left position. The reset position of the cursor combined with the absolute mode position reset of the tablet causes the cursor to jump. Sometimes the click/drag motion gets stuck and some object gets moved/dragged (media item, note, marker etc..).
Example 3 - VNC: I click a pan control and move it to max left position. Sometimes causes desyncs of cursor position that require resetting the server!
Example 4 - Application cursor control (such as osculator tied to a wiimote): I click a pan control and move it to max left position. Letting go of the drag operation can either cause a desync (cursor no longer matches physical device's pointing vector) or the cursor will jump around momentarily.
When using "Use pen/tablet-safe mode -- do not reposition mouse cursor while adjusting knobs/etc...", the mouse cursor ideally should not disappear when clicking on a control.