  Double white dwarfs are important gravitational wave sources for LISA, as
they are some of the most numerous compact systems in our universe. Here we
consider finite-sized effects due to tidal interactions, as they are expected
to have a measurable impact on these systems. Previous studies suggested that
tidal effects would allow the individual masses to be measured, but there was a
subtle error in those analyses. Using a fully Bayesian analysis we find that
while tidal effects do not allow us to constrain the individual masses, they do
yield informative lower bounds on the total mass of the system. Including tidal
effects is crucial to the accuracy of our estimation of the chirp and total
mass. Neglecting tidal effects leads to significant biases towards higher chirp
masses, and we see that the lower bound of the total masses is biased towards a
higher value as well. For many systems observed by LISA, tidal effects can lead
to a "stealth" bias, since only the first derivative of the frequency can be
measured. To separate tidal effects from the usual point particle decay we need
to be able to measure the change in the second derivative of the frequency
cause by the tides. This can only be done for high frequency systems observed
with high signal-to-noise. The bias, if not accounted for, can have significant
astrophysical implications; for example, it could lead to an incorrect
estimation of the population of potential Type IA supernovae progenitors.
