I think this is VERY common.
I frequently flip flop my kids names, I know my mom does as well.
Yesterday I was telling the dog to lay down because he was running all over the livingroom. His name is Forney. I said, "Little P LAY DOWN." Little P is my grandson! TOTALLY not the same thing AND he was also in the room!
I frequently call my 5 year old by her 21 year old sisters name. Last week I referred to my boyfriend by my 12 year old son's name! (no not during sex!).
The most memorable I think was an evening my husband and I were having an argument. He was being a real jerk, we were recently together and I am fairly certain he had been drinking. I called him by my most recent ex-boyfriends name.
We both caught it and silence ensued. Shortly thereafter he broke the silence with a comment about how he supposed he was acting enough like my ex to warrant that remark (not realizing it had been an accident).
Later I explained that it was an accident. But-it stuck in both of our minds and a strong reminder that if we behave like a familiar person-our minds connect us to that person.
I understand the sense of "hey I want you to KNOW its me you are with when we are together". It's one of the reasons I don't care to mix dating and drinking.
But, it's important to realize that even if we know precisely who we are talking to-sometimes the wrong name comes out. Furthermore, when we are talking to/about people with similar places in our lives, we may get all of those things crisscrossed too.
I read an article-either in October or November Psychology Today regarding "slips of the tongue" and how they can manifest. A lot of it was basic biological "oops"-as if we reached into the wrong file cabinet and spoke before we managed to grab the right file.
I say-let it go. Talk about it-find some humor in it-take it as a compliment.