Bluetooth Stutter (improved, but not completely fixed):
Overview: Open the system and ensure the antenna connections are tight and the card is seated well.
I found a bit of a fix looking through the forums. Essentially you open up the bottom of the laptop, and check to ensure the card is seated propperly and the antenna cables are connected well. Mine were a bit loose, and adjusting them has signifigantly reduced my issue. Ocassionally I still get a blip in the audio, but for the most part it's working well. Opening the thing takes only a few minuts if you have the tools (search youtube), and I was informed by Lenovo that this would not void the warranty so long as I didn't cause any physical damage.
Remaining Stutter:
The blip may very well be a result of a buffer issue relating to the DPTF throttling (i'm in tent or tablet mode most of the time I use bluetooth). I need to do more testing.
Unknown USB Device (Device Descriptor Request Failed) (Fixed!):
Overview: Go into the bios, disable wireless, reboot into windows, then shut down, go back into bios, and re-enable wireless.
I had an issue where after disabling bluetooth via the device manger, re-enabling it, and then rebooting, the bluetooth device showed up simply as; "Unknown USB Device (Device Descriptor Request Failed)". No software solution would work (drivers for both wifi and bluetooth, windows updates, ect...). This is not surprising, at it very clearly seems as though the hardware was is some mode that makes it unrecognizable to the system.
After a lot of research (other people have had the issue with this card on other systems), I decided to go into my bios in an attempt to reset the state of the card. I had seen some other post in a microsoft forum mentioning a method involving swapping out the lenovo power manager on 8.1 for the windows 7 version, then disabling->reenabling wireless with the old power manager fixed the issue, and so i thought maybe something in the bios would work instead. In the bios I selected disable wireless, rebooted, and it was back (even though my bios had the wireless disabled...). I am on the latest lenovo bios in case anyone wants to know. I went back into the bios and re-enabled wireless anyway, and the fix still worked.
Hopefully the Lenovo team will read this and figure out the issue, for I suspect it's bios and power management related. Two things about this that are really odd:
1. Setting the system into airplane mode didn't have the same affect. This indicates to me that the wireless card isn't being disabled fully in airplane mode.
2. Setting the wireless state in the bios to disable didn't disable the device and in fact re-enabled it. Toggling the state back to enable didn't change anything.
*I should state that I didn't try disabling it after the fix to see if it acted normal again, and it is possible the card just got into an unexpected state, sending the disable command resolved it, and now it will function as intended.
Wireless Coexistance (reply to a comment from OldSpaghetti):
Thanks for the post. I'm and embedded firmware and hardware engineer who does a lot of RF work. You are right in assuming this could be a potential issue, but unless they did an incredibly poor job with the antenna, I highly doubt it's a hardware related. They do a lot of RF testing, (including coexistance tests), with these chips before putting them out, and so asside from the case of a bad antenna, it's safe to assume this isn't a hardware issue. Drivers and firmware dictate how hardware functions, and so that is much more likely the culprate. Windows 8.1's power management, intel's drivers (wifi and bluetooth), the motherboard bios, and lenovo powermanagement software all play a role in controling the hardware. If there is a coexistance issue, I'd bet it's driver related.
Furthermore, I bought my laptop recently, and it has the 7260AC card in it, and this card is proven to work perfectly fine in other systems (though I have seen reports that early driver releases for these cards were problematic up until midway through this year).
With respect to swapping out the cards, I have no doubt replacing the WiFi card resolved your issue, for it had different drivers, and in swapping it out you reseated the wirelss card and the antenna connections.