FontForge can't even understand the simplest possible compact CID-keyed font

[ctrlcctrlv]

My title assumes a CID-keyed font is any font with a cmap table. I'm not sure if that's true, but I emailed a few people who might know. If they reply I'll update this issue.

Let's also say, FontForge created the font it can't understand!! This CID-keyed font stuff is stressing me out. 🤐

Let's make the font first:

1. New font
2. Encoding→Re-encode→Custom
3. Encoding→Remove Unused Slots
4. Encoding→Add Encoding Slots…→1
5. Draw a square (or whatever) in the new glyph
6. Right-click the glyph, «Glyph Info…»
7. Set name to percent, then «Set From Name»
8. Under «Alternate Unicode Encodings» put U+00A7, leave Variation Selector at 0
9. Save SFD as brokencmap.sfd, generate font brokencmap.otf.
10. Quit FontForge

Now let's see how broken our new font is.
KFontView understands it just fine as a font with two glyphs, percent and section:

Let's open our font back in FontForge…Open OTF and do «Encoding→Compact».

Go to Metrics View, then enter %§:

Looks good, but the FontView displays two percent signs, both with encoding U+25.

brokencmap.zip