Final tests:
For 3.6.0-beta2(.post3) all relevant data-types (float,int,bool,string) worked as expected.
For 3.5.4 with dsf-python-3.5.0 setting string-data and accessing it via "echo ..." also works.
So issue solved for me - merci!
Thx @all for their support to answer questions and find/solve issues!