Ok, thank you for this report. I'll include script to update this field size in next version.
Here is quick fix:
ALTER TABLE `jos_jcomments` CHANGE `ip` `ip` VARCHAR(39) NOT NULL DEFAULT '';
ALTER TABLE `jos_jcomments_votes` CHANGE `ip` `ip` VARCHAR(39) NOT NULL DEFAULT '';
ALTER TABLE `jos_jcomments_reports` CHANGE `ip` `ip` VARCHAR(39) NOT NULL DEFAULT '';
Don't forget to replace
jos with your site's table prefix (if you've changed it).