That's not a "problem", but a scenery FEATURE, and of course it's explained in the manual, and it's called FAROS:
http://rwsl.ll.mit.edu/DFW/FAROS.htmlThe blinking PAPI indicates the runway is occupied. In this case, by your own airplane, but it works for AI too.
You might be mislead thinking it's a "bug", because no other sceneries out there have those features, which are made possible by the fact PAPIs in our later sceneries are 100% custom, driven by the Couatl Python scripting engine.