mine have done the same thing. mine are just over 1 month into vegetation. they do it every time i bump up the fertilizer. and then i sit them outside for run off. maybe the direct sunlight for about 30 minutes, or bumping nutes or just feeding and sitting outside. it does the plant no harm, so far. mine are in containers and please note: be careful how you sit pots/containers down...you may put the plant in root shock if not sitting the pot down softly.
BUT WHOA-UP WAIT THINK ABOUT THIS!! it can be either one or two things..heat and/or a slight over fertilization.