  Blazars show optical and $\gamma$-ray flux variations that are generally
correlated, although there are exceptions. Here we present anomalous behaviour
seen in the blazar 3C 454.3 based on an analysis of quasi-simultaneous data at
optical, UV, X-ray and $\gamma$-ray energies, spanning about 9 years from
August 2008 to February 2017. We have identified four time intervals (epochs),
A, B, D and E, when the source showed large-amplitude optical flares. In epochs
A and B the optical and $\gamma$-ray flares are correlated, while in D and E
corresponding flares in $\gamma$-rays are weak or absent. In epoch B the degree
of optical polarization strongly correlates with changes in optical flux during
a short-duration optical flare superimposed on one of long duration. In epoch E
the optical flux and degree of polarization are anti-correlated during both the
rising and declining phases of the optical flare. We carried out broad-band
spectral energy distribution (SED) modeling of the source for the flaring
epochs A,B, D and E, and a quiescent epoch, C. Our SED modeling indicates that
optical flares with absent or weak corresponding $\gamma$-ray flares in epochs
D and E could arise from changes in a combination of parameters, such as the
bulk Lorentz factor, magnetic field and electron energy density, or be due to
changes in the location of the $\gamma$-ray emitting regions.
