Because minor amounts of XP are awarded for getting posts saved by other users, a security measure is in place to ensure that people are using the functionality properly, and not abusing the system in any way. It is also a highly resource intensive feature, especially in the Save Items Feed in your home feed area. However you have nothing to worry about as the amount you are given is typically enough for most users, and limit (and restoration speed) goes up as you reach higher XP levels.