On Safari 8.0.6 very weird comportement of classic layout="row" layout-sm="column"
<div ng-controller="AppCtrl" ng-app="MyApp">
<div layout="row" layout-sm="column">
<div flex>
I flex to one-third of the space on mobile, and two-thirds on other devices.
</div>
<div flex-gt-sm="66">
I flex to two-thirds of the space on mobile, and one-third on other devices.
</div>
</div>
Try this way
Okay,
Now i think safari failed to calculate the height of the first

Faced the same issue.. Fixed it with
[layout-sm=column] {
display: block;
}
You must set an explicit height
md-content div:first-child { height: 400px; }
on
<div ng-controller="AppCtrl" ng-app="MyApp">
<md-content >
<div layout="row" layout-sm="column">
<div flex="75" flex-sm="33">
I flex to one-third of the space on mobile, and two-thirds on other devices.
</div>
<div flex="25" flex-sm="66">
I flex to two-thirds of the space on mobile, and one-third on other devices.
</div>
</div>
</md-content>
</div>
Here is a CodePen Demo with
Fixed in SHA e8b60de997fc06e1471d9e30a2e0f300bc18869f
@robertmesserle - am i missing anything with my CodePen? Can you see any way to avoid explicitly setting the height of the mdContent?
If your container doesn't have a fixed height, why would you want to use flexbox at all for stacking elements? I'm not sure what the expected outcome is.
Here is a working solution using ngMaterial Layouts (with flexbox) and media transitions:

<md-content layout="row" layout-sm="column">
<div flex-sm="34" flex="75" class="md-whiteframe-z2">
<div class="desktop overlay">
<span>flex=75</span>
<br><br>
Three-fourths (3/4) viewport size on larger devices.
</div>
<div class="mobile overlay">
<span>flex-sm=34</span>
<br><br>
One-third (1/3) viewport size on mobile
</div>
</div>
<div flex-sm="66" flex="25" class="md-whiteframe-z2">
<div class="desktop overlay">
<span>flex=25:</span>
<br/><br/>
One-fourth (1/4) viewport size on larger devices.
</div>
<div class="mobile overlay">
<span>flex-sm=66:</span>
<br/><br/>
Two-thirds (2/3) viewport size on mobile
</div>
</div>
</md-content>
Live with Source on CodePen Demo
There's here is explained that happens.
Most helpful comment
Faced the same issue.. Fixed it with
[layout-sm=column] {
display: block;
}