This may be a bit hard to explain, as it's a very odd bug.
So I make a panel that contains a "table" gameobject with table attached, and inside that assorted buttons and labels. The panel is at 0,0,0; it has clipping on, centered at 0,0. Everything "lines up" with the sprite box underneath it.
The "Table" game object located at -150,255,0 (since otherwise half the contents will stick out of the panel). the contents all line up perfectly.
Now, if I hit reposition now on the UITable (currently doing this in inspector), it LOOKS like nothing has changed, but actually it does something odd:
It moved the panel to 4.999985,15,0 and sets the "center" in UIPanel's clipping settings to -4.999985,-15. With different paddind in the table, it changes the numbers it shifts to.
The expected behaviour is for the clipping and the panel transform to stay put.
This is a somewhat minor bug, since it *visually* doesn't change things, but if you are setting up panels in specific locations, having transforms that shift to apparently random numbers causes all sorts of problems.
(P.S. Congrats on the hire! I look forward to seeing what you do with Unity UI now that you've got your hands on the source!)