I"ll be damn! Look what I started!I'll be hornswaggled and dipped in Bantha poodoo. You're right: Kirk's wearing the same buckled boots:
Further: it appears on inspection that both Shatner and his stunt double are wearing the boots with buckles. Neither Gary Lockwood nor his stunt double wear them. In fact, their boot design seems closer (though not identical) to those used on the series.
Maybe they were just off the rack.
Dakota Smith