No backup possible – Error: Is a directory

A problem plagues me with nice regularity: it happened just now when i wanted to write a backup.
If I want to make a backup copy of my drive, the installer (i’m using the installer app for this job) stops everytime at “kdeinit5_” because “Error: Is a directory”.
I tested different partitions, drives and other applications, which changed nothing.

However, when I search for “kdeinit5_”, I get no hits (a similar question has appeared in the forum already, but also without a solution.) I suspected that Calligra could be the offender and kdeinit would belong to this package. But unfortunately that did not help anything. Any ideas?

What haiku revision do you use? This should have been fixed in https://git.haiku-os.org/haiku/commit/?id=hrev53483 by @waddlesplash.