You probably have inference snapping enabled, which changes the middle button to Get Snap since your single left click would be used for snapping based on the Dynamic Snapping settings. You can turn off Inference Snapping in the Program Preferences, Drawing tab under Dynamic Snapping. With Inference Snapping off, middle click will be normal snapping once again SHIFT+Middle Click will bring up the Get Snap menu when needed.
Thanks! - Josh Do. Or do not. There is no try. Josh's Digital Downloads is come back online soon. Stay tuned. (soon is a relative term)