Detailed progress reporting not working with adaptive update bundles

[BubuOT]

Describe the bug
The more detailed progress reporting currently seems not to be working with adaptive update bundles:

 70% Checking slot rootfs.1
 73% Checking slot rootfs.1 done.
 73% Copying image to rootfs.1
 99% Copying image to rootfs.1 done.

Background information
Rauc 1.10.1
System image/update bundles built with buildroot.

To Reproduce
Steps to reproduce the behavior:

1. Create a bundle with adaptive=block-hash-index
2. Install to a target

Expected behavior
Rauc produces intermediate progress reporting while updating a slot. Instead rauc only prints the next progress line after updating a single slot is done.

Logs
See above.

Additional context