Maybe not a bug, more of a minor UI feature request
You can’t create an input pin inside an IF region
But if you have some patching and you marquee select it and then use Surround>IF you can indeed end up with an input pin inside the IF region. This can occasionally happen by accident if you are putting a large quantity of nodes into an IF region.
In this case nodes won’t execute (or won’t return results at least) but there is no error which would make it easy to identify this problem.