Tumblr adds "denied" to the beginning of Skype URI link in a caption

Question

I was trying to include a Skype URI link in a Tumblr caption like so: skype:echo123?chat

But when I submitted the post, the link was: denied:skype:echo123?chat

I've included Skype links in the past this way with no problem, so I have no idea why I can't do it with this post. I've used different Skype accounts, removed "chat" and made it "call" instead, and the same thing happens.

Where is this "denied" coming from, what does it mean, and how do I fix it?