Altium 16, wierd problem clicking on traces when interactive routing

[supdude]

I've been using Altium for years and this just started happening recently.  The scenario:

1. have a partially routed trace
2. click the interactive routing button
3. click on the partially routed trace

Sometimes it works fine, sometimes altium assigns the new routing to "No Net" and it doesn't connect to the trace I'm trying to route (video demonstrating the problem: https://ibb.co/ktdJ6H).  Anyone seen this before?  It seems to be completely random as far as I can tell. 

Deleting and re-routing the trace from a pad fixes it, but it's pretty annoying!