FBO with NPOT textures on Opengl ES 2.0

I need to use NPOT textures using off-screen FBO for rendering.

The problem I’m facing is that images rendered on the FBO are all messed up ONLY under certain texture sizes.

If I use textures sizes such as 640x640 or 320x240, the FBO will render fine. But, if I use a 480x320 or 480x480, the FBO renders a garbled mess up of the image.

I’m using GL_CLAMP_TO_EDGE in the texture setup so it should allow to use any texture size.

Any explanation for that?