using 2 textures in GLSL

[rpreininger]

I' testing mix of 2 textures, but only the first one is used.
In the ressource manager both are displayed and binding is 0 and 1.
But in this simple fragment shader:

uniform sampler2D tex0;
uniform sampler2D tex1;

..
vec2 uv = gl_FragCoord.xy/uResolution;
vec4 color0 = texture(tex0, uv);
vec4 color1 = texture(tex1, uv);

outColor = mix(color0, color1, 0.5);

only the first one is used.
Thanks
Ralf