Are backslashes not working in your WordPress posts? The most likely reason for this is due to a WordPress plugin. The best solution is to disable your plugins one by one and check to see if your backslashes come back.
Backslashes – WordPress
We are currently having issues with the SEO Smart Links plugin and currently have it disabled, as this was removing our backslashes from all of our posts.
We have opened a post on their forums here: http://www.prelovac.com/vladimir/forum/plugins/seo-smart-links-plugin-removing-backslashes#p3284