Trying to create a polygon between points using the "Fill" mode on the topology pen mode does not work, instead, it moves one of the vertices to where you clicked.
Steps to reproduce
1) open modo with the Topology tab 2) Select Topology Pen 3) set the mode to points 4) put out four points to act as corners of a quad 5) set the mode to Fill 6) Hover the mouse between the four points and you will see a face highlighted, indicating that you can create a polygon there 7) RMB click the quad > One of the vertices moves to where you clicked
Observations: - It does not matter if used with a background mesh as the tool is intended for or not. - It seems that what is actually happening is that Move mode is turned on even though Fill has been set