This is Microsoft's problem.
Late in 2011, Microsoft made the decision to change the way data was provided to app-writers (including their internal apps group). Without going into the technical details, the cloud-based part of Bing doesn't communicate properly with the older Bing app for Windows Mobile. The actual implementation of this change started rolling out early this year, and was finalized in early June 2012.
Since Windows Mobile 6.x is considered a "legacy" system by Microsoft now that it has Windows Phone 7.x (and 8.x coming soon), they are just not going to do anything about it on Windows Mobile. We're stuck with the last working version of Google Maps for Windows Mobile (at least, that still works for me).
Considering how popular Windows Phone was 2-3 years ago (before the iPhone and Android took over the mobile world), it's somewhat surprising to me that almost NO ONE complained about this. And as long as no one is complaining, bugger-all will be done to fix it.
Anyway, reference this discussion on the Microsoft Answers forum: http://answers.microsoft.com/en-us/winphone/forum/wp6n-wpdevices/bing-on-windows-mobile-65-internetg...