Just a heads up. It looks like Yahoo Mail pushed an update that changes width to min-width in email campaigns, which has an impact on hybrid emails. Looks like Nicole Merlin stumbled upon the issue which has been verified by a few others. Our designer, Kevin, looked into it a bit and saw the same, but was able to come up with a temporary fix. In the head of your document, you can add a Yahoo-specific media query that overrides that bit of CSS:

<head>
<style>

@media yahoo { 
  .foo {min-width:300px!important;} 
}

</style>
</head>

Just swap out the 300px with whatever your original, desired value for width was.

Would love to hear if anyone else is seeing the issue and if there are any other fixes.