The default texture minification filter is GL_NEAREST_MIPMAP_LINEAR, which is all well and good if you are using mipmaps, but useless if you aren’t and your texture is being drawn small enough to need the minification filter.
I don’t ever expect these incompatible defaults to be fixed… it would be a breaking change.
I first encountered this a few years ago when I started out with OpenGL and it took me a while to work out. I also struggled to debug this problem last night… since searching the internet and these forums proved practically useless I decided to post it up here.
Changing the minification filter with glTexParameteri to GL_LINEAR fixes the “problem”.
Why GL_NEAREST is not the default is beyond me though…