Hello and thank you for the demo!
Glyph is not visible in this case because ImageList converts a glyph to the 32-bit bitmap with empty mask (so, glyph is drawn with mask using but pixels are invisible because alpha value is 0).
You can look this glyph if save him to the disk from the glyph property.
I'll try to solve a problem in the AlphaImageList component, but I haven't idea how to affect a standard imagelist…
Of course, TsSpeedButton haven't such problems.