wx.SplitterWindow. SplitHorizontally is ignoring the third argument if this is negative
It looks like the default window size in wxMSW was changed from (20,20) to (400,250). The wx.SplitterWindow has a feature that if the window is currently too small for the specified sashPosition then it assumes that the window hasn't been resized to it's full size yet and the value is remembered. Then in the first resize event that sash position set and all is well. Now that the initial size of the window is "big enough" then it doesn't worry about saving and resetting.
I'll ask about this on wx-dev but in the meantime the workaround is to specify a small size for the wx.SplitterWindow.
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Robin Dunn
Software Craftsman http://wxPython.org Java give you jitters? Relax with wxPython!