[RPi3] cannot apply device tree overlay

[Niklas]

Hey,
as of the latest linux-raspberrypi upgrade, I can no longer use device tree overlays. Since the dtoverlay option in /boot/config.txt has never been working in the first place (which is another issue that needs fixing), I created a simple oneshot systemd service to use /opt/vc/bin/dtoverlay. I am using the pi3-miniuart-bt overlay to switch the uart input to /dev/ttyAMA0. Unfortunately, applying the overlay now fails with the following error:

$this->bbcode_second_pass_code('', 'Feb 19 00:32:31 home kernel: OF: overlay: Failed to apply single node @/soc/gpio@7e200000/fake_bt_cts
Feb 19 00:32:31 home kernel: OF: overlay: apply failed '/soc/gpio@7e200000'
Feb 19 00:32:31 home kernel: create_overlay: Failed to create overlay (err=-22)')

This breaks my home automation system. Would be nice if somebody could help me out.