Audio [Q] Bluetooth headset button event not handled properly?

I'm using Nexus 4 with stock 4.4.2, rooted, and iSimple BluStream (find BluStream on the Bestbuy site - no links here, sorry) as the handsfree/A2DP bluetooth device in my car.

The device works perfectly fine - it pairs both as a headset and as a media receiver at once. However, it has only one hardware button, and pressing this button always results in redial (when not in call), answer (during incoming call) or hanging up (when in call).

I tried all apps I could find, such as Headset Button Controller, Headset Droid and JAYS Headset Control trying to assign different actions to clicks, double, triple clicks etc.

Neither one works.

Regardless of an app and its settings the headset button always invokes either redial, answer or hangup.
All these applications have "monitor" mode that allows to see headset button events it receives. Neither application sees any headset button click at all, like the headset is bypassing the apps! All apps also have "check for conflicts" option that checks if any other app has top priority to receive headset button clicks - and all apps always say "no conflicts".

media_button_receiver in Settings storage -> settings.db -> system changes accordingly to the launched app - it shows either JAYS Headset control or audioplayer - whichever is running.

There are also four bluetooth_headset_priority parameters in Settings storage -> settings.db -> global, with four different MAC addresses and the values of 100, 100, -1 and 1000.

Anyway, my problem is that regardless of what I do (install various button remapping apps, change settings etc.) the headset button always behaves like it is hardwired to redial/answer/hangup.

I tried to google around (including this forum), but still have absolutely no clue, like I'm the only user having such problem.

Any ideas are much appreciated!