CSS の指定方法に関係していました。CSSをこれに変更すると、期待どおりに機能しました。
/**** Isotope CSS3 transitions ****/
.isotope,
.isotope .isotope-item {
-webkit-transition-duration: 0.8s;
-moz-transition-duration: 0.8s;
transition-duration: 0.8s;
}
.isotope {
-webkit-transition-property: height, width;
-moz-transition-property: height, width;
transition-property: height, width;
}
.isotope .isotope-item {
-webkit-transition-property: -webkit-transform, opacity;
-moz-transition-property: -moz-transform, opacity;
transition-property: transform, opacity;
}
/**** disabling Isotope CSS3 transitions ****/
.isotope.no-transition,
.isotope.no-transition .isotope-item,
.isotope .isotope-item.no-transition {
-webkit-transition-duration: 0s;
-moz-transition-duration: 0s;
transition-duration: 0s;
}
/* End: Recommended Isotope styles */
/* disable CSS transitions for containers with infinite scrolling*/
.isotope.infinite-scrolling {
-webkit-transition: none;
-moz-transition: none;
transition: none;
}