I'm not sure if there's been a change recently, but it seems like the site is no longer remembering which tags I've used when editing the tags on an image. Usually it would remember the tags I've used for what seems like about 30 minutes or so, but now it no longer saves any tags.
When trying to figure out the issue, I did see that in my profile you can make a list of quick tags. However sometimes while tagging I'll spot something I normally don't tag very often and use it, but it's a little annoying that it's no longer getting saved for the next time I'm going to apply it.
Was this a site update change or is there something going on with my browser? I'm using firefox if that helps.