Hello,
some BarCode controls such as "Code 39 Extended" and "Code 25 Interleaved" require a TwoWay binding of the "Text" property when used in a MVVM scenario. (And some do not, such as "Code 128")
It took us several hours to find that out.
My suggestion is to improve the documentation for this behaviour.
In the demos and documentation only a fixed text is used.