Kernels 4.19+ on Arch break local keymap support in systemd-based plymouth decryption screen for LUKS
I am using plymouth (via plymouth-git from the AUR) on Arch in conjunction with GDM on a disk that is configured as LVM-on-LUKS. Initramfs generation on Arch is handled via a tool called mkinitcpio, which assembles the initramfs from building blocks specified by the user. I have mine configured to build an systemd-based initramfs, including i.a. plymouth, my local keymap, and the systemd-decrypt blocks.
Up until the release of kernels 4.19+ (I am also seeing this on 4.20rcs) this setup worked well. However, starting with 4.19 I noticed that the decryption screen displayed by plymouth no longer supported my local keymap (de-DE) but instead acted as though an en-US keymap had been embedded into the initramfs. This is somewhat annoying, as my LUKS passphrase contains some characters that are awkward to produce using a US keyboard.
Strangely, though, the initramfs for the lts-kernel (4.14.x), made with the same tool, using the same plymouth version, continues to behave as before. An initramfs without plymouth will also support my local keymap.
Is there any way for me to debug this?
System config: kernel 4.20rc5 systemd 239.303-1 mkinitcpio 25-1 plymouth 0.9.4.r41.gf7d5bb12-1