How can I safely switch on and off glAccum() func?

DELETE IT: IT was a completely different problem.

Right now I’m trying implement basic motion blur,

it works fine,

glAccum(GL_MULT, value);
glAccum(GL_ACCUM, 1-value);
glAccum(GL_RETURN, 1.0);

If ‘value’ is changed or changed to 0 it works but I’d like to avoid the overhead and just not let the functions be called.

But when I do switch the functions from not being called at all to being called and vice vera, the app crashes.

What does it need front or back?