Bad rendering in Portal Linux beta

I get a strange rendering problem in Portal on Linux (via the latest Steam beta).

I'm running on integrated Intel HD4000 with fairly recent modules/drivers (up to date Arch). Everything is smooth and there's no crash, but some objects seem to be transparent and others are almost completely black.

For example the first thing I see in the new game looks like this:

On the console, I can see some shaders / materials failing to load (missing):

 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/maps/background1/c-1369_-576_368.vtf
 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/maps/background1/c-1536_-768_368.vtf
 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/maps/background1/c-1561_-384_368.vtf
 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/maps/background1/c-1561_-564_181.vtf
 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/maps/background1/c-1561_-576_368.vtf
 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/maps/background1/c-1696_-544_368.vtf
 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/maps/background1/c-1776_-624_368.vtf
 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/models/weapons/v_models/v_hands/v_hands.vtf
Error: Material "___fillrate_0" uses unknown shader "FillRate"
Error: Material "___debugnormalmap_1" uses unknown shader "DebugNormalMap"
Error: Material "___debugdrawenvmapmask_2" uses unknown shader "DebugDrawEnvmapMask"
Error: Material "___debugdepth_3" uses unknown shader "DebugDepth"
Error: Material "___debugdepth_4" uses unknown shader "DebugDepth"
Error: Material "debug/debugluxels" uses unknown shader "DebugLuxels"

 ##### CTexture::LoadTextureBitsFromFile couldn't find materials/models/weapons/v_models/v_hands/v_hands.vtf
Error: Material "models/humans/female/pupil_r" uses unknown shader "Eyeball"
Error: Material "models/humans/female/pupil_l" uses unknown shader "Eyeball"

Any ideas whether this is fixable on my side?

I had the same problem with almost the exact same system. Installing libtxc_dxtn and lib32-libtxc_dxtn fixed it.