In the three 1.8.6 apps and current 1.9 betas on macOS, option key has no modifying effect when using backspace key to delete a node of a curve. Option key should result in the app attempting to preserve the shape of the curve when a node is deleted, but only simple node deletion is happening, the same as when only the backspace key is pressed.
I checked in APub 1.7.3 on macOS, and option key with backspace key is effective there: the app does attempt to preserve the shape of the path.
I will post a bug report if nobody can solve this puzzle by tomorrow.