[Exim] system_filter uid/gid error

Hello list,

I've encountered a problem with the system_filter.

Up to version 4.21 no problem at all, but now I get the following
error with version 4.22:

unable to set gid=200 or uid=600 (euid=75): system filter

I have specified:
system_filter_user = 600
system_filter_group = 200

If I use it without these options I get later on an error. The error
than occurs when the pipe transport (defined in the system.filter)
gets executed with the following error:
unable to set gid=200 or uid=600 (euid=75): local delivery to <...rest.of.command...> transport=filter_pipe

In the filter_pipe I've set
user = 600
group = 200

Any ideas what's going wrong?

Regards,
Christian