It’s not rare that a major versions introduces some bugs. so, Polylang 1.5.1, released last week, aimed to fix problems with date archives links, posts bulk edit and some bad redirection for sites having /language/ in their permalinks which were introduced in Polylang 1.5. Also, several older bugs, including some issue with the nav menus in customizer, were fixed. I also attempted to support the function ‘switch_to_blog’ used in multisite.
I would have waited several weeks to publish a new maintenance release, but some hours ago, Gregory Viguier reported a security issue and I believe that it was worth to quickly release a new version to fix it.
Also WPML to Polylang 0.1.4 was released in the same time as the links created between translations were removed after the first post update. It worth to notice that user feedback is very important to get this plugin better as I personally don’t use it. So far, at least one user reported a successful migration from WPML 3.1.5!