Keyboard cues are disabled by default on newer versions of Windows. Some win32 common controls, e.g., button doesn't draw a focus rect when SystemParametersInfoW(SPI_GETKEYBOARDCUES) reports FALSE.
Drawing a focus rect when the button is really small creates an effect that makes the button look corrupted. On Windows, the focus rect is not drawn when keyboard cues are disabled, which is the default.
Other controls also have this behavior, so they're included as well. There are some exceptions, for example, SysMonthCal32 always draws a focus rect, even when keyboard cues are disabled.