I’ve seen this phenomenon before and there is probably a simple answer, but I cant figure it out, so someone please solve this mystery for me.
Sometimes a poster will post something like this.
But when someone else quotes their post, their username changes like this.
What gives?
Ddsun was her original name. I’m guessing that pay was before she changed it. So at the time she was quoted, the names matched. Once her name changed, so did the original post, but not the quote.
Right, the username is changed for posts, but not when a user is quoted under their old name.
I saw a sorta similar thing today. I searched for and read an old post of mine. Which had my sig enabled on it. But the sig that displayed on this years-old post is the one I use now, not the one I’d used then when I posted. The new sig doesn’t fit the theme of the old post even a smidgen.
The wonder of cheapo database design is that our posts as displayed now are a mishmash of what was written then, and stuff pulled from the database as of now.
This mixing of now-data and then-data is a big issue in real commerce and government databases. But is often skipped over as “too hard; not enough benefit to bother avoiding” in lesser applications.
The OP’s shifting usernames is an example of that, as is my mysterious time-shifting sig.
SIG text is not part of the post. It’s fetched when a post is rendered and will always represent your current SIG. Usernames aren’t part of posts either, all that is kept is the user ID, and the text printed is fetched from your profile. Quotes are stored as text and don’t change over time. It’s not that complex, you just need to know what is in which of two categories.
And you need to know that vBulletin’s [del]cheap[/del] simplistic database design doesn’t keep effectivity dates on data values and hence only knows about “now”, not the relevant "then"s.
One of the many delights of using outdated board software. 
What’s “cheapo” or “simplistic” about doing it that way? The simplest way to do it would be to store all of that information in the post itself. You only get dynamic information like vBulletin has if you do it deliberately.
Meanwhile, it’s impossible to dynamically update quotes like that, because quote tags can contain anything at all, including material sourced from outside of the board. So the only way to keep track of those is in the post itself.
Quite the contrary. Your old sig stopped being effective when you changed it, and so it’s no longer used.
Thanks for the explanation, guys. I figured there was some logical explanation, but changing usernames didn’t even occur to me.