2.1.1358 Part 1 Section 188.8.131.52, grpSpPr (Group Shape Properties)
a. The standard states that bwMode is a valid attribute on the grpSpPr element.
Excel and Word do not support the bwMode attribute on this element.
b. The standard does not describe the relationship between group shapes and their child shapes with respect to bwMode.
In Office, bwMode set at the group level should set bwMode for child shapes.
c. The standard states that the bwMode attribute specifies that the group shape should be rendered using only black and white coloring.
Office uses this attribute to specify how the group shape should be rendered when in black and white mode.