I've looked around quite a bit for a solution to this problem, but haven't found anything that works yet, nor anyone talking about it for Joomla 3. Most posts about this online are years old and for Joomla 2.5, and none of them actually offer a solution.
The problem is that every time I save a menu item, it then produces a "404 - Category not found" screen, and the url changes from myurl.com/alias-here to myurl.com/Category/alias-here. This started happening after an upgrade from 2.5 to 3.3 (and the site is currently upgraded to the most recent version). The site was also upgraded from 1.5 about 2 years ago and worked fine for that time.
The temporary fix that a lot of people are doing, is doing a menu "rebuild" at the top of the menu manager. That does work, but it's not a good solution for website with lots of changes and additions being made daily, because every time you save one, you have to remember to click the build button. It seems like this might be a bug to submit??
Anyone experience this and know a fix??? I don't get stumped often, but I'm really not sure about this one.