D2: The designer added visual properties to my non-visual component!

I have discovered that, when I subclassed "TDataModule" (a non-visual
component) and did not add it to the VCL library, the designer automatically
added non-visual properties (Font, TextColor, etc) to the DFM file which the
component does not have.

No errors are reported at design-time; the form opens quite normally.  But at
runtime everything goes to hell in a handbasket real-quick-like.  :-(