See screenshot:

Using latest version 1.1.2.1. Tested with/without optifine. Testing without/without texture packs. Problem persists. Most likely not an issue with the texture itself.

Small question, are you using Immibis connected texture mod ? I had problem with both glass and IC2 glass before when I used it...

Yes, for this test world I had Immibis' connected glass mod. Removing/disabling the mod seems to fix the problem.

Then problem solved, you can yell at Immibis to fix this xD I had the same problem before though since he is only here once a year now, you might have some trouble to yell at him xD, not from our side at least xD may you close this ?

Go ninja'd :3

I'll go let him know. For now i'll just used Optifine. Speiger beat me to closing the issue :P

XD just saw: close this thing and i was at home for about 2 minutes. So i closed it