Hi Jean,
It's annoying isn't it?
Two suggestions. First, the end of the path is trying to snap to grid, so
you can try switching off "snap to grid" while you're adjusting the path.
Second is something I've found useful. Let's say you need a horizontal
path. If you adjust the right hand end of that path, that right hand
endpoint is no longer exactly horizontal with your left hand end point. So
if you now click on the left hand end point, and move it slightly it will
also snap to the grid and (hopefully) the path will now be horizontal again.
However, you may find that the entire path is now either too high or too
low, and when you run the animation your object will seem to jump up or down
before moving. To correct this, click on the path and hold down the Control
key while you use the up or down arrow to nudge the path back where it
belongs.
I don't know if anyone else has a more systematic approach. I've found it's
a bit of a hit and miss exercise, but you will get there in the end.
Cheers,
Geoff