Using slant transformation on VF leads to bad sidebearings

Glyphs
1

Using

{
customParameters = (
{
name = PreFilter;
value = "Transformations;Slant:10;SlantCorrection:0;";
}
);
}

on a static font:

image
image878×376 2.91 KB

and on a variable font:
image
image878×376 2.92 KB

Any reason for this?

2

Force an origin with value 3. Might help a little bit. Why PreFilter?

3

Because using Filter has even worse outcomes on composites.

4

Okay, I have found what triggers it: unnesting nested components, which is done in an export plugin. If I unnest components manually beforehand, the export works fine.