No suitable flow variable present - Python Node Development

Hello KNIMErs!

I stumbled across this (minor) issue whilst developing my nodes.

Whenever I want to use flow variables, whilst using already established nodes, I get this error message:

No suitable flow variable present

It seems that this message occurs whenever I use my own node and a KNIME node simultaneously.

Is this behavior wanted by KNIME?
Will this behavior change when a node is published?

Thanks!