It is. I’ve been to two of those. I mean, not super-fancy weddings, but “we had to get legally married previously, but now we’d like to celebrate with you, our friends” events."
Having a wedding reception later is fine, especially if you couldn’t do the big public (perhaps church) ceremony. But having the big ceremony much later, after you were already married in a civil ceremony, is wrong. Basically it’s a performance.
I went to one that was in a church, with a minister. Technically, they renewed their vows, I guess. The minister certainly acknowledged that they were already married. But it was important to them to make vows in public, in front of their friends and family. I don’t see anything inappropriate about that. I feel that marriage is a public status, and making vows in public is meaningful.
Hmm, actually, I can think of two more such events that I’ve attended. So I guess I’ve been to 4. The weirdest was the one where half the guests were gay and the couple apologized for having gotten legally married (privately, by a JP) when they knew that many of their friends could ONLY have the sort of ceremony they were having. (This was before same-sex marriage was legal, of course.)