Andrew,

Tested on 3.27.6 Win7 32bit msi, replicated on 3.32.4 (trial), probably OS independent.

A bit similar as linetypes before ;-) ... (FS#2622)

It seems that the list of patterns in the Hatching dialog is based on whether the document unit is considered to be metric or imperial.
Disregarding this is ambiguous for RS::Microinch (FS#2541) but that unit is probably best handled as 10-based like all metric units.

We would expect that the list is according the document measurement system.
It is not: Current implementation is whether doc unit isMetric or not.

But there is more to it:
With a custom pattern installed in the metric folder,
with a new empty document in mm, with the measurement system set to imperial,
the (metric) pattern is listed in the pattern drop-down list of the hatching dialog.

The preview is empty and the resulting patterning is also empty.

However, on saving such a file and after reloading, the patterning is shown as intended.
Pattern type is 'from entity' ...
... And can thus not be used for creating a new Hatch with that pattern.
Except new blank ones ...

Somewhere down the line the pattern is correctly sourced from the
RPatternListImperial resource list and stored in the DXF.

---

Background:
For a ready to donate Zig-Zag pocketing Add-On I need an available, measurement system / unit independent and immutable custom pattern.
Exploiting the QCAD hatching engine to do a lot of the work.

But it seems I can not generate a virtual custom RPattern (Q 11971).
Nor construct one from RPatternLine objects.

I must thus rely on an installed pattern file. :-(
Identical for both systems but also mutable and removable ...
... The problem is retrieving that with 100% certainty or the Add-On can't pocket.

Regards,
CVH