In his recent post Gonzalo Ayuso shares some "strange behavior" he found with method visibility in his recent development:

Normally I feel very comfortable with PHP, but not all is good. There's some things I don't like. One is the lack of real annotations and another one is this rare behaviour with visibility within the OO. Let me explain this a little bit.

The problem came up as a part of a recent refactor where a protected method, when called from an object injected into another class, threw an "access" error that it was called from the wrong context. He reported it as a bug but was reminded of how PHP handles exposure - on the class level, not the instance of a class level.