Always? That generally happens when its a new item that you haven't had in your inventory before so the client takes a little longer to find the image. If it never finds it, even with multiple client restarts, then it sound like those files might be missing. At that point I'd suggest deleting all your client files and downloading the client again.
@mvgulik There have been cases where ppl got corupted DLs from Ender mediafire url (encountered it myself - guess it's a provider/routing prob) - using the oddity url solves it...
to OP just run the default client once for some minutes to get the .haven cache updated with missing icons (res) had helped me
Avatar by SacreDoom Java 8 - manually downloads - good to check for actual versions url here: viewtopic.php?f=42&t=40331 Remember what the dormouse said: Feed your head Feed your head