  New observations of variable stars in the globular cluster M3 reveal that the
RR Lyrae variable V79 is a double-mode (RRd) variable with the first overtone
mode dominating. In all previous studies, V79 was found to be a fundamental
mode (RRab) pulsator with an irregular light curve. This is the first observed
mode switch for an RR Lyrae variable and it is direct observational evidence
for blueward evolution of horizontal branch stars in the Oosterhoff type I
cluster M3. It also demonstrates that there is a connection between the Blazhko
effect and pulsational mode mixing in RR Lyrae variables. These new
observations also show that the strength of the overtone oscillations in the
RRd star V68 in M3 may have increased in the last 70 years, thus indicating
blueward evolution for V68 as well. A survey of previously published
investigations of RRd stars in Oosterhoff type II systems indicates that there
is marginal evidence for an increase in the strength of fundamental mode
oscillations in two stars: V30 in M15 and AQ Leo. If these increases are
confirmed by future observations, it will indicate redward evolution for RRd
stars in type II systems.
