transform + overflow:scroll + iframe: element not painted

[paulrouget]

<style>

.a {
  transform: translateX(0);
}

.b {
  height: 400px;
  width: 400px;
  background: red;
  overflow: scroll;
}

</style>

<iframe src='data:,x'></iframe>

<div class='a'>
  <div class='b'>
  </div>
</div>

[notriddle]

This can be reproduced without actually using an iframe

<style>

.a {
  transform: translateX(0);
}

.b {
  height: 400px;
  width: 400px;
  background: red;
  overflow: scroll;
}

.c {
  background: green !important;
}

</style>

<div class='a'>
  <div class='b'>
  </div>
</div>

<div class='a'>
  <div class='b c'>
  </div>
</div>