Coordinates of nodes messed up

I am running Inkscape for win 32 on win 7 64.

I find something very frustratting: if you take 2, you add 3, then you subtract 3, you expect to have 2 again?

Well, Inkscape says not to that. All coordinates move in strange ways. I set them at exact points, and when I do some operation, something as banal as changing the fill of the drawing, when I check again at the nodes, they have been displaced.

Now x coordinate instead of being, say 145.000 it's 145.003 or 144.982 or something like that.

Why is that hapenning? I don't understand why the software needs fo mess up with coordinates for very simple operations. It's very frustrating having to police for nodes, seeing if Inkscape hasn't start moving them around!!!

Why is it so difficult to program a software that understands that 2 plus 3, minus 3, equals 2, and not 1.98 or 2.03 or some aproximate value?

Regards,

FE