From review at https://github.com/keymanapp/keyman/pull/9405/files#r1289675373

Some frame keys cause a context invalidation. Frame keys and modifier keys etc then get kicked back to the OS, but any US English character-generating key gets added as an action

ldml processor doesn't do this yet.

Also see https://unicode-org.atlassian.net/browse/CLDR-17262 we may need some spec improvement here.