  We study the reaction $e^+ e^-\to \omega\pi^0$ in the vicinity of $\phi$ mass
region. The isospin-violating $\phi$ excitation is accounted for by two major
mechanisms. One is electromagnetic (EM) transition and the other is strong
isospin violations. For the latter, we consider contributions from the
intermediate hadronic meson loops and $\phi$-$\rho^0$ mixing as the major
mechanisms via the $t$ and s-channel transitions, respectively. By fitting the
recent KLOE data, we succeed in constraining the model parameters and
extracting the $\phi\to\omega\pi^0$ branching ratio. It shows that the
branching ratio is sensitive to the $\phi$ excitation line shape and background
contributions. Some crucial insights into the correlation between isospin
violation and Okubo-Zweig-Iizuka (OZI) rule evading transitions are also
learned.
