Do you have any plugins installed? please post a test login so I can see your comments box. I would suspect based on the numerous threads on this issue that it is a hack conflict and disabling the plugin that is causing this will solve your issue.
Chuck, I do not have any plug-ins installed. At least I'm pretty certain I don't. I installed one for vBulletin to cut down on the spammers, but nothing has been installed unique for photopost.
Use test / testing123
Please be aware though, that only two folks are seeing the one-character box. The rest of us see a bigger box.