I just set the meta tags (title, keywords and description) for a category on my site. These changes were made via the Zen Cart Admin.
Since I was only testing things I decided to remove my changes. I simply deleted the title, keywords and description entries and hit the save button.
Then, when I refreshed my site I noticed that the category page had blank meta tags. All other category pages and non-category pages display their meta information correctly.
So, this appears to be a bug.
Apologies if this has already been reported - I did have a quick search before posting, but found no similar issues.
Bookmarks