Will Bainbridge authored Jul 18, 2017 and Andrew Heather committed Jul 18, 2017

Tracking through an inverted region of the mesh happens in a reversed
direction relative to a non-inverted region. Usually, this allows the
tracking to propagate normally, regardless of the sign of the space.
However, in rare cases, it is possible for a straight trajectory to form
a closed loop through both positive and negative regions. This causes
the tracking to loop indefinitely.

To fix this, the displacement through inverted regions has been
artifically increased by a small amount (1% at the moment). This has the
effect that the change in track fraction over the negative part of the
loop no longer exactly cancels the change over the positive part, and
the track therefore terminates.