I did in the early days of the system, and I think it was because I'd reloaded the merit pop-up screen after giving someone merits--it's been so long that I can't recall what happened, and I do believe that problem was fixed (but I could be wrong).

Not a big deal if you've got enough merits to send, though it's definitely annoying to hand out extra merits when you didn't mean to.  I don't think it was your fat fingers, btw.  Mine are like shredded pepperoni sticks and I still manage to not make the mistake I made way back when.