Really strange behaviour browser issue, Comments will save in Safari but will not save in Firefox or Chrome or on Linux Firefox/Chrome, Not tested on Windows.
Zenphoto 1.6.4

Since the comments functionality is server side this would be really strange. Please review the logs.

Nothing in the logs to show any errors that I can see, the only thing on Chrome I get a deprecated error
Unload event listeners are deprecated and will be removed
source tinymce.min.js:2

Try to disable tinymce for comments.

Tried that and no change, Safari works fine

Then I have no idea, sorry.

What file is the printcomment function located in as I want to try and find the reason. I have had a look but cannot find that particular function. It must be to do with my hosting as I get get the same behaviour with the unstable version.

Most functionality is within the comment_form plugin but parts are also in core files.