slicing fails when there are multiple parts with tabs

[carlneilson]

When there is 1 STL file with multiple parts in it with tabs added, slicing fails ; it gets stuck at 0%. Without tabs, the slice operation completes.

The same parts separated into 4 STLs with tabs added works (but the rough operation fails to clear stock properly).

[carlneilson]

The parts that are being sliced are hexagons. It turns out that slicing also fails with 1 STL with 1 part in it if the part is oriented with a vertex pointing left and one right at the Y axis. Rotate it by 30 degrees to have a vertex pointing up and one down at the X axis, then the slicing works.