Background images not showing when using GLES 2

After switching to

ofGLESWindowSettings settings;
settings.setGLESVersion(2);
ofCreateWindow(settings);

images are not drawn anymore on Android. I have switched to this syntax because GL ES wasn’t activated and I couldn’t use shaders on Android. Now, it seems to me that fragment shaders are working, but textures aren’t.
I checked in OFAndroidWindow.java but it’s beyond my knowledge.
Even if the shader seems to work, I get all these

E/ofShader(12921): bindDefaults(): trying to link GLSL program, but no shaders created yet
E/ofShader(12921): linkProgram(): trying to link GLSL program, but no shaders created yet

in logcat.
Any opinion?

Note: this may or not be related to the problem I posted of some days ago, solved:

Note n.2
Same log, different problem here.