Hi Lauren,
Are you using "Lead Status" as a filter? My sales team gets alerts not when a score is changed but when a lead status is changed. Which is based on a lead score moving up; whenever a lead reaches 50, the lead status changes to Marketing Qualitifed and that's when they get emailed.
So you could set up a campaign that monitors the lead score, and changes the lead status. If the lead status doesn't change, then sales won't get emailed. Otherwise, I think to have "lead scores = 50" makes sense.