winfo rootx and rooty on Aqua appear to be returning values that are relative to the top left corner of the toplevel in 8.4.19, rather than the top left corner of the screen. [winfo rootx .] and [winfo rooty .] both return 0 wherever the toplevel is moved on screen.
I noticed this while migrating from Tile 0.7.6 to tile 0.8.2, when I found its combobox was behaving very badly (not responding to clicks in the popdown except to hide it, and popdown placed in the wrong place after moving the window the combobox is in). But after trying to isolate the issue to changes in Tile, I found it was doing this in my released app, too, which was recently upgraded to Tcl/Tk 8.4.19 (but still Tile 0.7.6). It was at that point that I found that rootx/rooty are returning bogus values in 8.4.19.
This was previously working with 8.4.9, so I believe this to be a regression somewhere between 8.4.9 and 8.4.19.