  We report additional photometric CCD observations of KPD 0422+5421, a binary
with an orbital period of 2.16 hours which contains a subdwarf B star (sdB) and
a white dwarf. There are two main results of this work. First, the light curve
of KPD 0422+5421 contains two distinct periodic signals, the 2.16 hour
ellipsoidal modulation discovered by Koen, Orosz, & Wade (1998) and an
additional modulation at 7.8 hours. This 7.8 hour modulation is clearly not
sinusoidal: the rise time is about 0.25 in phase, whereas the decay time is
0.75 in phase. Its amplitude is roughly half of the amplitude of the
ellipsoidal modulation. Second, after the 7.8 hour modulation is removed, the
light curve folded on the orbital period clearly shows the signature of the
transit of the white dwarf across the face of the sdB star and the signature of
the occultation of the white dwarf by the sdB star. We used the Wilson-Devinney
code to model the light curve to obtain the inclination, the mass ratio, and
the Omega potentials, and a Monte Carlo code to compute confidence limits on
interesting system parameters. We find component masses of M_sdB = 0.36 +/-
0.16 solar masses and M_WD = 0.47 +/- 0.16 solar masses (M_total = 0.86 +/-
0.35 solar masses, 68 per cent confidence limits). If we impose an additional
constraint and require the computed mass and radius of the white dwarf to be
consistent with a theoretical mass-radius relation, we find M_sdB = 0.511
+0.047 -0.050 solar masses and M_WD = 0.526 +0.033 -0.030 solar masses (68 per
cent confidence limits). In this case the total mass of the system is less than
1.4 solar masses at the 99.99 per cent confidence level. We briefly discuss
possible interpretations of the 7.8 hour modulation and the importance of KPD
0422+5421 as a member of a rare class of evolved binaries.
