The release appears to be quite buggy, hasn't been well tested
Windows Phone 8 might not be set to arrive on all devices that already run under Microsoft’s mobile operating system, but Windows Phone 7.8 will make current WP users a bit happier.While there’s no word on when the platform will actually arrive on devices, owners of an HTC HD7 smartphone can already download and install the platform upgrade.
Windows Phone 7.8 beta ROM was made available for them, though with a series of issues, as you’d expect.
The ROM features build 7.10.8835.35, and has been compiled based on a Tango 12180 dump from a Nokia phone. Unfortunately, it was not tested intensively, and those who download and install it will do so at their own risk.
Undoubtedly, a better release will arrive on HTC's device in the not too distant future, and users might want to wait for that one. Not to mention that the official update might be close as well.