Update from my end here, as people are going down the pathetic rhetoric road again.
Reverting to Maverics did not help.
Reverting to Alkaline batteries did help. Not always, but very much did it improve the situation.
Yes, it did reoccur at times, but a lot lot less. Which rather indicates, this is kind of a power supply problem to the devices, probably aggravated by other effects like system load, etc. (just guessing), and certainly already present in late Mavericks.
Yes, there are many things to whine about. For example, recently all my IDevices start ringing when I get a phone call. I ended up turning off FaceTime entirely on all devices. I'm using Skype anyway. And I don't like Apple apparently making things even more uncomfortable for people by "inviting" them to split one family used iOS account to multiple accounts for each family member. And I don't use the "aaawwwesomme" new feature called handsoff, since the voice is apparently so much muffled that I can't use it. Or rather, I could, if I wanted to connect my headset directly to my laptop and not to my thunderbolt hub, using, yes, bluetooth again or rather a cord. Which is why that's not entirely off topic perhaps.
There's probably only one thing that I really don't like with Apple - they keep telling people what they should do and how they should do it. That is, if you think about it in terms of leadership theory, completely last century. The reason I stay with them is that on the other hand, if I invest the extra time and resources, I can end up using the devices mostly the way I want, and as an add on get an awesome feature set. I sometimes just think I am just too old to understand some of the "so simple" features. Like why does ITunes insist on one particular space for the media library should the folder where I have it not happen to be there? If I put the library on one of my servers, and am not connected, it will create a new media library silently, and then it will import the next songs that I put over there - with a very manual way of moving things over as their media library again is in some binary format. Why does it keep making backups of my mobile devices even though I told it not to? I keep scanning my hard drive like every month or so and look for "big things" that have just accumulated. But that's perhaps things that won't happen to a "normal" user anyway who stores all his content on his internal drive and buys a bigger device the moment that overruns. Yet I'm not alone in my family, so my Lightroom folder needs to be shared and accessible for everyone, my music, pictures, videos etc. also.
That's nothing to do with bluetooth, but since people get in a ranting mood, why not throw some more stones. No women over here anyway, or are they? Blasphemy! By the way, one practical thing I'd like to share, just because I found it to be pretty cool, when speaking about a shared lightroom folder, I've tried ownCloud for a while now, and am using it intensively. Put the lightroom catalogue there, and share it. The pictures can stay on some server. The lightroom folder can have the previews. Depending on my device, I have the lightroom catalogue either on the internal SSD - like my wife has that as she doesn't use the laptop for as much other things as I do - or on an external disk, like the awesome Lacie Little Big Disk, an 1 TB SSD.
Just my three cents.
Use alkaline batteries, really.