Inside PRoot (ARM) : script (without shebang) terminates with Exec format error

[willi....@gmail.com]

I played a bit with proot 5.1.0 (x86_64) on ubuntu 10.04 and a recent raspbian image.
The command line was
 proot -q qemu-arm -S raspbian-root -b raspbian-boot:/boot /bin/bash

when doing apt-get upgrade I got an error for package wolfram-engine.
The error came from a post-install script which has no shebang line.

Further investigations:
created hello_word.sh without shebang:
Error while loading ./hello_world.sh: Exec format error
With shebang #!/bin/sh all is ok.

How to avoid this error?
Thanks,
Willi