> Here is what the TrueType reference manual says: [...]
Found it! It's not a bug but a feature. From file
`src/truetype/ttobjs.c`, lines 1048ff:
```
/* UNDOCUMENTED! The MS rasterizer doesn't allow the following */
/* graphics state variables to be modified by the CVT program. */
exec->GS.dualVector.x = 0x4000;
exec->GS.dualVector.y = 0;
exec->GS.projVector.x = 0x4000;
exec->GS.projVector.y = 0x0;
exec->GS.freeVector.x = 0x4000;
exec->GS.freeVector.y = 0x0;
exec->GS.rp0 = 0;
exec->GS.rp1 = 0;
exec->GS.rp2 = 0;
exec->GS.gep0 = 1;
exec->GS.gep1 = 1;
exec->GS.gep2 = 1;
```
This is commit a2c7eb188892c6 from 2013, confirmed then by Microsoft
engineer Greg Hitchcock.
I've just filed
https://github.com/MicrosoftDocs/typography-issues/issues/1012
so that it gets documented in the OpenType specification.
Werner
