With its mandatory download requirement and perceived invasiveness, Facebook Messenger has already caused its fair share of consternation among Facebook mobile users. But the app could become an even bigger lightning rod for criticism after it was found to seemingly censor links to porn sites at random, according to a blog post at Reason.com.

The story came from Cleveland comedian Walter Hemmelgarn, who tried to share a video of someone drumming which happened to be hosted at Xvideos.com, one of the largest porn sites on the web. However, when a user tries to share a link to Xvideos in Facebook Messenger, they receive this message from Facebook in reply: “The content you’re trying to share includes a link that our security systems detected to be unsafe. Please remove this link and continue.”

Now, Facebook doubtlessly has good intentions for blocking porn in its new app. However, they only do so selectively; according to the blog post at Reason.com, many porn sites, including 4tube, Badjojo and Bigtube, are not blocked. What’s more, porn sites don’t necessarily pose any more of an inherent security threat than many other websites do.

As is so often the case with Facebook, the privacy rules it sets for its users make sense, but its enforcement of the rules proves spotty at best.