On my site, when I start typing tags, the autocomplete works but then when I make a selection or hit enter I get lots of commas.

For example, I start to type "lands" and the auto complete shows "landscape". Now when I make a selection, the input box shows.

la,,,,,,,,,landscape,

Any ideas?

What browser is used? Have a link maybe? Never noticed that, just to note.

Maybe I have an idea, but since I do not know what version of Zenphoto you are using, who knows.

The version is 1.4.0.2 and I tested the following and saw the same issue. (sorry the site is on an intranet so no public url..)

Mac OSX: Chrome, Safari, Firefox
Windows 7: Chrome, Internet Explorer
CentOS 5.4: Firefox

More detail: when I hit enter to do the autocomplete, the string that I typed, [partial tag], isn't replaced but appended to plus several commas before the autocompleted tag, [autocompleted tag]

Like this:
[partial tag],,,,,[autocompleted tag]

A bit more info... I started to look at the html,

<input type="text" name="words" value id="search_input">

Maybe this is the location in the tag_suggest plug in that is having an effect? I'll try to tweak that line and see what happens...
http://www.zenphoto.org/trac/browser/branches/development/zp-core/zp-extensions/tag_suggest.php?rev=6721#L45

Install 1.4.0.3

That fixed it! Thought I had the latest version, you guys release fast ^_^