Safariでborder-radiusとtransitionが組み合わさるとおかしくなる

<div class="thumbnail">
    <img src="sample.jpg">
</div>

.thumbnail {
position: relative;
  width: 250px;
  height: 250px;
  border: 2px solid #ccc;
  border-radius: 125px / 125px;
  overflow: hidden;
  z-index: 1;
}

.thumbnail img {
  -webkit-transition: -webkit-transform 0.3s linear;
  -moz-transition: -moz-transform 0.3s linear;
  -o-transition: -o-transform 0.3s linear;
  -ms-transition: -ms-transform 0.3s linear;
  transition: transform 0.3s linear;
  z-index: -1;
}
.thumbnail:hover {
  border: 2px dotted #ccc;
}
.thumbnail:hover img{
  -webkit-transform: scale(1.1);
  -moz-transform: scale(1.1);
  -o-transform: scale(1.1);
  -ms-transform: scale(1.1);
  transform: scale(1.1);
}