Resolution problem on external display with Thunderbolt->HDMI adapter Let me explain problem in quick bullets:

What I want:
I would like to use ultra wide external display with 3440x1440@50hz resolution with my MacBook Pro (Retina, Mid 2012).
I would like to use my Thunderbolt port on mac, and my HDMI 1.4 input on my display.

I can successfully connect my display using:
- HDMI -> HDMI with 3440x1440@50hz
- TB -> DP (via TB -> DP adapter) with 3440x1440@50hz

I can partially successfully (with limited resolution) connect my display using:
- TB -> HDMI (via TB -> HDMI adpater) with 1920x1080@60hz (max)

Question is:
Is it matter of my adapter? For me it seems like it doesn't support HDMI 1.4, but only lower standard. (I have no idea how to check adapter type/support. There was no information about that on the product box).
Or maybe that is basically not possible to convert signal properly with TB/DP -> HDMI adapter?

Please advise.
Thanks,
Tomasz

P.S.
I have MacBook Pro Retina (Mid 2012), GeForce GT 650M 1024MB, OS X El Capitan (10.11.3).
It is the OS update; it includes system protection protocol so Apple is limiting your options of choosing the refresh rate in order to prevent system failure. Instead of fixing the bugs they just take away possibilities.