@fredrikekre & @mkitti
First of all thank you for your help! 
It was haphazardly that I included the function Tulip.__init__() in my minimal example
and it was not obvious to me that this was already the part of the Tulip-code that causes the trouble.
Ok, I understand the root cause of my problem. Consistently, I have added my local clone of Tulip.jl as development package to the primary environment, but this does not cure the problem 
During package compilation the standard Tulip.jl is taken to build the library “sys.dll”.
Is there a way to specify the local Tulip.jl-package to be utilized during package compilation?