I've noticed this. But, you have to look at the tiny text at the bottom. Has the topic been edited? Did the owner decide they liked the design too much and can't delete the topic? That, or they could post their character(s) as a family member to the adoptable characters (such as a parent or sibling).
There are multiple scenarios you have to play. For example, I was intentionally making a character to adopt out yestarday. However, I liked the design too much and decided to build a character - thus evolving my new character
"Diamondback." That, or they just want to flaunt their character(s). A lot of people know that, if you post in the Adoption area, people are more likely to look at their topic(s). Therefore, attracting attention to their subjects.
I could be wrong - there could be something else. But I believe I have it analyzed well. -Shrug.- If anything,
don't flame the user. Politely correct them and report the topic to a moderator as "wrong section."