Some Android devices don't work multi Render-To-Texture physically?

Some Android devices don't work multi Render-To-Texture physically?

I'm trying to run one program which has two render-to-textures (two
textures).
It is working all my IOS platforms( 3gs, 4, 4s but not simulation it is
also weird )
and working at four Android devices of six , the two devices which is not
working have SGX 540 , 544 GPU.
Actually, these two render-to-textures are for blur effect.
So the first RTT function always produces a new RTT1.
And second RTT function uses the RTT1 and makes it cloudy for blur effect
and also produces RTT2 ( in short, the second RTT function is accumulating
every frame )
I think the main problem is RTT2 is not accumulated at all in some Android
devices.
They can't keep the RTT2.
This is the procedure.
function1() for RTT1
{
draws main images on Offscreen1
}
function2() for RTT2
{
draws blur effect with RTT1 and RTT2 on Offscreen2
Shader code : gl_FragColor = (RTT2*0.90) + RTT1; // accumulating every
frames
but in some Android devices , RTT2 has black screen and only draw RTT1.
}
Rendering()
{
function1(); // produces RTT1
function2(); // uses RTT1 and produce RTT2
draw(); // draws RTT2 on OnScreen (but only RTT1 in RTT2 is drawn
according to (RTT2*0.90) + RTT1 )
}
Now I suspect some devices can't keep two RTT.
Do you have any ideas or same experience ?