Please note attached 3DM files to recreate this bug

In "Extrusion bug A", the indicated curve is selected and Extrude is attempted in the negative direction. Nothing happens.

If the various pieces are moved into the positive quadrant, the indicated curve can be extruded in a negative direction.

There is some kind of problem with a double point, at the bottom.

Hi Yenmonger, thanks for reporting this bug - that is kind of weird that it works in one direction and not the other but it does seem to be a side effect of that area that Brian shows above - the bottom curve of the shape is a polyline made up of 3 segments and the middle line segment is a really teeny tiny little line piece and that's having a bad effect on the whole operation.

In the attached version I've put just a single line across that bottom area and now it should behave normally.

- Michael

Place a new line across the bottom, in red.
Zoom way in with top view.
The two central points are not on the red line, in other words,
the item is Not quite planar.

Very good, thanks!

I've noticed sometimes when points get too close together a red square is drawn around them - is there a way to expand this behavior to this case? That would help me realize that I had a 'bad' curve to work with.

Hi Yenmonger, the tricky part is that it's somewhat difficult to know for sure which particular size is the cutoff for what is going to cause a problem with a particular operation.

The red square is drawn only when control points are stacked almost exactly on top of one another (within 1.0e-24 units of each other).

A curve segment one would need to be a lot looser than that, and with looser warning thresholds there is the chance for false positives.

- Michael