Tab character doesn't display

This is a screenshot of Unexpected keyboard with extra keys enabled, showing the tab character on the top-left of the a key.

And here is an equivalent screenshot showing a white box in the same place, with the same layout. The character is still functioning, just not displaying properly.

Additional info:

• Device: OnePlus 6T
• OS: PostmarketOS edge with sxmo
• Version: git main as of 42bb1137
• Layout: latn_qwertz_cz.xml from right here