TEdgeSlip causes warning diagnostics to be generated in TRect constructors and/or TLayoutWindow::Layout due to denormal rectangles in the layout. See e.g. our Classes example.
This happens during slip insertion (TEdgeSlip::DockableInsert calling DockableMove, calling CompressGridLines, calling ReLayout, which finally calls TLayoutWindow::Layout) and window setup (TEdgeSlip::SetupWindow calling ReLayout, calling TLayoutWindow::Layout).
Note that the slip appears correct in the end, due to later Layout calls (from TDecoratedFrame::SetupWindow and TLayoutWindow::EvSize). However, it seems the layout logic assumes fully constructed windows, and hence fails to work as intended before and within setup.
Also, in addition to correcting and making the layout logic more robust, the many repeated and likely superfluous Layout calls from construction to final resize should be further looked into and streamlined.