Weight Editing Weirdness

[JimmyAngler]

So i've noticed this a couple of times, but I never thought of it as too serious until it actually showed up as a visual flaw.
I remember weight editing a body awhile back to perfection, like every point was perfect.
Now, when i open the scene in xsi, some of the points change to strange mixes of the nearest bones.
Like the leg will have points with 95.4/4.6 for a couple points around the knee, when i clearly remember making them 100.0/0 when i first edited them.
Any ideas?