[Designer] Moving a single vertex in face mode moves the wrong vertex.

[Vhwatgoes]

Grabbing a single vertex in face mode may select and move a different vertex or many additional vertices.

 Video Example

In this demonstration, the design is sitting at 65% of the allowed data limit as I attempt to adjust some vertices. Notice the response times before a change is finally made to a vertex.

I select a Vertex, drag to move it, and one of 3 things happens:

1. The vertex I selected is moved normally.
   
2. The vertex I selected moves, but several new vertices are now selected too.
   
3. The vertex I selected does not move, instead several other random vertices move in the same direction and distance I tried to move the single vertex.
   

I seem to reliably get a grip on the program when I select a few other vertices to kind of 'reset' my selection. After that I have a good chance I will get the intended result. Not sure if this actually does anything but it's become my ritual.

The more vertices I move without doing this, the higher chances an error seems to occur, with more errors each time.