Subworkflow: Buffer --> Execute failed: Invalid projection

Hi,

I have issues with a Buffer Node in a Callee-Workflow: the workflow works fine without a Container Input Node, however, when this workflow is called by a caller workflow, I get this message, no matter what projection I choose:

Buffer 6:5: Execute failed: Invalid projection: … (Internal Proj Error: proj_create: Error 1027 (Invalid value for an argument): utm: Invalid value for zone)

This is quite annoying, as the workflow works normally without being a subworkflow.

Caller:

Callee:

Any ideas how to solve this? Thanks a lot in advanced.

Caller.knwf

Callee.knwf