# interpolationWeightY breaks instance and export in Glyphs 4

**URL:** <https://forum.glyphsapp.com/t/interpolationweighty-breaks-instance-and-export-in-glyphs-4/37337>\
**Category:** Glyphs\
**Tags:** bug\
**Created:** [September 23, 2026, 4:01pm UTC](https://forum.glyphsapp.com/t/interpolationweighty-breaks-instance-and-export-in-glyphs-4/37337 "2026-09-23T16:01:41Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![ammazzarella](https://forum.glyphsapp.com/letter_avatar_proxy/v4/letter/a/cdc98d/32.png) [@ammazzarella](https://forum.glyphsapp.com/u/ammazzarella)\
**Post date:** [September 23, 2026, 4:01pm UTC](https://forum.glyphsapp.com/t/interpolationweighty-breaks-instance-and-export-in-glyphs-4/37337/1 "2026-09-23T16:01:42Z")

</div>

When an instance has the interpolationWeightY parameter set, it doesn’t show up in the preview (it defaults to a master instead) or in the text preview (I get an exclamation mark with an ‘unknown error has occurred’ message). Exporting also stops at the instance before the broken one, nothing after it gets exported.