Why can't I decompose this glyph?

In this glyphs file the tehMarbuta-ar.fina glyph Light layer can not be decomposed when I run Glyph > Decompose Components.

Why is this?

It does decompose for me in v851.

I’m using Version 2.3b (854)

@davelab6, if you are using a custom GlyphData.xml, check that the components that compound the glyph are declared in the GlyphData.xml under the decompose entry.

This is how tehMarbute-ar should look:

<glyph
   unicode="0629"
   name="tehMarbuta-ar"
   sortName="ar1050"
   decompose="heh-ar, twodotshorizontalabove-ar"
   category="Letter"
   script="arabic"
   production="uni0629"
   altNames="afii57417, tehmarbutaarabic"
   description="ARABIC LETTER TEH MARBUTA"
   anchors="top, bottom"
/>

Best,

Nicolás

the decompose entry in the glyph data is something else. It is actually used of the opposite, build the glyph from components. The name is a bit misleading.