What should happen when a flag is deemed valid?
The merge has to be manually performed by a mod -- in this case they manually marked the flag as valid but didn't merge yet, so it could be any amount of time. Possibly they decided the posts can't actually be merged, but they marked the flag valid because it was a good suggestion; in that case they'll never be merged
Mods don't always have to act on a flag. But we do want to get that flag out of the queue if nothing needs to be done.
So a mod looked at your flag, said, "its a valid suggestion, but I don't think the two are close enough to merge." So, rather than being me and marking your flag invalidI hate your flag weight they marked it valid and then just moved on.
Sometimes mods have to act. Sometimes we should act. But the majority of the time flags exist in a nether realm where we could go one way or another, and so whether or not we act is based purely on subjective judgement calls. A perfect system.