I have not had a chance to look into it, but since you have been away on vacation, some things to note: fixes landing are targeting the 1.2 release that should hopefully be wrapping up some time in September. With that release, mozilla-central will be used for gecko instead of the b2g18 branch of gecko.

So you might try with the latest mozilla-central/gaia combo to see if that works better for this, as any bugs with the actual transition would need to be verified against mozilla-central anyway. How I updated my b2g build. From inside the B2G git dir:

* `rm -rf objdir-gecko` (or wherever your build output went, may be named differently on your device, probably has  objdir prefix)
* `BRANCH=master VARIANT=eng ./config.sh unagi` (i'm using unagi, change to your phone type, but note the BRANCH value)
*  `BRANCH=master VARIANT=eng ./build.sh`
* `./flash.sh`

Specifying both BRANCH and VARIANT may be overkill there, but I just do it out habit now.

There is now [preliminary devtools support working on the device now](https://groups.google.com/forum/#!topic/mozilla.dev.b2g/BzdyNs-WJj0), another reason to try out BRANCH=master. No inspector yet, but debugger is there. Follow the instructions in there and the special flag needed to build Gaia correctly for it. 

The `DEBUG=1 make` option for gaia is now much nicer too, since it outputs to a `profile-debug` folder instead of `profile`, so you can easily switch to desktop debugging and then back to on-device work.