An unrelated input polygon vertex disappeared after a union operation

When uniting the following two polygons
A: `POLYGON((-8 0,-10 0,-10 4,10 4,10 0,8 0,4 0,0 0,-8 0))`
B: `POLYGON((0 2,4 2,4 0,4 -2,0 -2,0 0,0 2))`

The union result is
`MULTIPOLYGON(((4 -2,0 -2,0 0,-8 0,-10 0,-10 4,10 4,10 0,4 0,4 -2)))`

But the expected result is
`MULTIPOLYGON(((4 -2,0 -2,0 0,-8 0,-10 0,-10 4,10 4,10 0,8 0,4 0,4 -2)))`

The vertex `POINT(8 0)` was erased by a call to `detail::overlay::append_no_collinear` inside of `travel_to_next_turn`. The expectation is that any input vertex lying on the result boundary must be a result vertex.

AFAIU, the problem was introduced in d0ca69a058. And according to the commit message the expected invariant holds.