Some info about SGCAPS flag in VK_TO_WCHARS1.Attributes

[DJm00n]

SGCap:  means that this key is affected by the Shift state and the CapsLock
    state, but in different ways.  This is described in two lines: the First
    is marked SGCap in column 3 and indicates how the character values are
    determined according to whether a Shift key is down or not.  The Second
    line is marked with -1 in column 1 (scancode) and indicates how character
    values for the same key are determined according to the CapsLock state.

If SGCAPS affects this key and CapsLock is on: use the next entry
in the table, but not is Ctrl or Alt are down.

http://kbdlayout.info/features/SGCAPS