We've recently upgraded to 5.4.2 and I'm finding that when we create a new post and add a tag such as #612, it doesn't save. I've also noticed that when I try and untick 'uncategorized' and tick News as Primary, that doesn't save either. I guess these could be related. I then checked on our staging site which is running 5.2.14 at the moment and find the same thing there so it may have been an issue for a while. This is a problem for us because we use the tags to route posts to the news pages of hundreds of member group pages and so none can currently publish to the website.
Any help would be much appreciated.