GA Code does not Save for AMP

Hi – I’m looking to enter my GA code for AMP pages here: https://dl.dropboxusercontent.com/u/88896/2016-05-08_1647.png … I’ve tried the normal Google Analytics script and just the UA code. Regardless, whenever I hit save the value is removed. I get a confirmation that “Settings Saved” but the value is blank. And a view source on the amp page shows no code added. Any tips? Thanks!

https://ww.wp.xz.cn/plugins/yoast-seo-acf-analysis/