Are you using workflow or check-in/out? If so, make sure you are checking in and publishing as the changes won't take effect until those processes are complete.
I've come across something like this before as well and in a few instances the above was the solution. Other instances there was some other page causing problems with either a space at the end of the field that created the URL or some invalid HTML. You might need to check the database and take a look at the URLs in there.
WHERE NodeAliasPath like '/images%'
From there you should be able to see the path and any document name info. You may then have to manually modify the record (very carefully) or you might find there is a ghost record in there with the same info that was not deleted. I've seen this as well and I believe its caused from Content Staging errors.