I'm using Google Ad Manager to fill ad slots, but I'm having an issue with one ad unit. If there's no ad available, it still stretches the container DIV out! And just leaves a big empty spot.

This wouldn't be tragic except that I measure the height after the document is complete, and if it's empty then I throw in an alternative. With it stretched out, though, I can't do that.

Here's my code, do you see any reason for it to be stretched out?

<style>
#block_3 {
 position: sticky !important;
 top: 0
}

.med_rect {
 width: 300px;
 max-height: 250px;
 padding: 10px;
 margin-bottom: 10px;
 border: 1px solid #E3E3E3;
 background: #F5F7F9;
}

<div id="block_2" class="med_rect"
 style="margin: 10px 0 20px 0; height: auto">
  <script>
  // tableWidth is set earlier, and shouldn't be relevant to this
  if (tableWidth >= 975)
   googletag.cmd.push(function() { googletag.display('block_2'); });
  </script>
  <div id="backup_2"></div>
</div>

<div id="block_3" class="med_rect"
 style="height: auto; max-height: none !important; margin-bottom: 20px">
  <script>
  if (tableWidth >= 975)
   googletag.cmd.push(function() { googletag.display('block_3'); });
  </script>
  <div id="backup_3"></div>
</div>

You can see that they're pretty much identical, but block_3 includes "max-height: none !important".

I don't think this should matter, but in GAM block_2 is [300, 250] while block_3 is [300, 600]. And they're both defined under the same googletag.cmd.push(function() { ... }) (in a loop), so there shouldn't be any different settings.