Sorry, but I really have no idea on this one, and I can't seem to find any way to duplicate this on my server, so I'm not really sure what to tell you.
Hopefully now that you have supplied a little more information someone else will recognise the issue and can offer a solution.
Meanwhile, it may also be prudent to let us know what version of zencart you are using.... if using an older version this may even be a bug that has already been fixed in one of the updates.
Other information that it may be useful for us to know include:
Is this a new installation? If not, has it ever worked 'correctly'? If so, when did the problem start? Have you added any modules that may have had an effect.
As I say, someone may simply recognise the symptoms and be able to give you a solution, but if not, then the more information we have, the better chance we have of isolating or identifying it.
Cheers
rod
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