Possible bug in Service regarding USERCULTURE() and Slicer

Hi,

I've having an issue with a client's report that's being translated to German.
I'm using USERCULTURE() on the slicer title conditional format using the code below:

IF ( LEFT(USERCULTURE(),2) = "de", "German Label", "English Label" )

In one page all is working ok but when I go to the next page/tab of the report it always detects USERCULTURE() as "en-US".
It's the same slicer on the same data. Not sure why this happens.
Here's a gif showing the error on the "Retailer" slicer:

Thanks for any help