There is a settable time that allows members to edit their posts - currently set at 5 minutes to allow members to nip back in and change any typos and the like. This again is to prevent people returning to delete their posts one after the other if they have thrown their toys out of the pram (which longer term members will know several incidents of). Once they take this petty course of action, topics can be incredibly hard to follow.
I do see that 5 minutes is way to short and will change that.