When you click the button that changes the step, the active tab is md-active, but its contents and bar are not shown as if they are not, which only happens after clicking a different tab and returning. The problem does not happen rendering from step 2
<div v-show="step == 1">
</div>
<div v-show="step == 2">
<md-tabs md-active-tab="nao">
<md-tab id="sim" md-icon="check" md-label="Sim"></md-tab>
<md-tab id="nao" md-icon="cancel" md-label="Não">
Conteúdo a ser exibido, só que não
</md-tab>
</md-tabs>
</div>