bicubic shader and scalehq shaders are inverted or crash rgui

[BrainDamage]

a bit long description since the problem is rather complex:
my setup is a linux optimus laptop, with both an intel and an nvidia chip
the bug is reproducible with any 2d core, threaded driver either on or off, git commit for rarch: 1754acb
several shaders such as anti aliasing do work correctly with either 1 or 2x scale
loading bicubic or scalehq shaders, with 1x scale, results in a 180° vertically mirrored image with either video chip
setting 2x scale with those problematic shaders, results in a correctly displayed image with the intel chip, but produces a crash in rgui with the nvidia one, once set to such shaders, any attempt to launch retroarch, even in the menu before the core selection, will result to a net crash with the nvidia driver

stacktrace for the crash:
http://codepad.org/9Pp4uB20

I can provide any additional info since the problem is 100% reproducible for me

[BrainDamage]

closed since i cannot reproduce anymore after updating retroarch and nvidia drivers