I use qtranslate for multi-language content, and recently experienced issues with a plugin that adds extra wysiwyg fields to posts and pages.
The content of the main wysiwyg editor was being overwritten with the content of the last wysiwyg editor in the page.
The fix for this issue that worked for me, is the one proposed by alexleonard in the qtranslate forum: http://www.qianqin.de/qtranslate/forum/viewtopic.php?p=12468&sid=c60a21e882af27f0fc0f038f0c6905a6#p12468
This seems to fix the problem for any plugin that adds wysiwyg extra fields, not only ACF.
Thanks to mgibbs189, plugin author of Custom Field Suite (by the way, great plugin!) I was able to find this fix.
I hope this helps others find the fix easily.
And it would be great if it could be added to the plugin in the future.