When editing a scripted expression driver by clicking in the button and typing (niiiice feature by the way), the driven channel doesn't change it's behavior till file reload.

To reproduce:

1- create a file with two objects (default file will do)
2- add a driver to one of the transforms of one of the objects
3- in the f-curve editor,add a new variable 'var' that is the transform channel of another object, but don't change the scripted expression from 0.00
4- the driver doesn't do anything
5- Now in the properties editor click on the driven transform channel and type 'var', enter.

Expected result:
6- the driver now works
Actual result
6- the driver still has no effect
7- save the file
8- reload it
9- now the driver works.

OS : GNU/Linux 64 bit (Ubuntu 10.10), Intel Quad core, nVidia gfx.
No test file since reloading fixes it anyway.