Designed behavior for multi-platform
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 * Radio buttons in Cocoa version does not work as expected unless the buttons 
   of a group are contained in a single container.
 * The gtk-1.X application sometimes falls in dead-lock on multi-threaded application.
 * Applications with narrow width sometimes have undesirable space on the right edge 
   of the window. This behavior is apt to appear on high-resolution PC.

Known Bugs
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 * The size of spTabBox depends on the tab size that is displayed firstly.
 * The buttons of spDialogBox is always aligned to left.
 * The background of a canvas of gtk version is not drawn correctly after changing the theme.
 * Gtk-WARNINGs are displayed on first initialization of spList on gtk version.
 * The scrollbar doesn't work correctly when the scrollbar is customized to
   overlay-scrollbar which is used in Ubuntu.
 * The cursor of a non-editable combo box is displayed after selecting that on macOS.
 * spPrimitiveSetSensitive from threads sometimes causes crashes on macOS.
