GCAL error?

Trying to render even a simple grid_block() with default options makes OpenSCAD throw:
```
ERROR: CGAL error in CGALUtils::applyUnion3D: CGAL ERROR: assertion violation! Expr: itl != it->second.end() File: /usr/include/CGAL/Nef_3/SNC_external_structure.h Line: 1084 
```

Surprisingly it seems to be working fine in preview