Widget Anchor Initialization

The Widget Anchors go through different stages of initialization:

VARIABLES_LOADED
At the time your frame recieves this event, its anchors are initialized to the values in the xml file.

PLAYER_ENTERING_WORLD
When handling this event for a frame which parent is UIParent, World of Warcraft deletes all anchors and loads the layout data from layout-cache.txt. If the frame layout data have not been saved in the cache (the user has never moved the frame with the mouse), Frame:GetLeft, Frame:GetBottom, Frame:GetRight and Frame:GetTop return nil.