SVG foreignObject not working in Vue 2.1.5

[anthonyjl]

SVG foreignObjects were working after the #4122 fix but have been broken again.

Vue.js version
2.1.5

Reproduction Link
https://jsfiddle.net/oqctnm08/

Steps to reproduce

• Run it once as is
• Once without var vue = new Vue({ el: '#body'});
• Once with version 2.1.4 instead of 2.1.5.

What is expected?

• In version 2.1.5 you will see no text inside the rectangle.
• When you run it without Vue the text will work fine.
• In version 2.1.4 the text will also be fine.

What is actually happening?
Some change between 2.1.4 and 2.1.5 reverted the fix to this.