When I created forum, I puted that it dont save sent messages, now I want to change that, and I did, but even if it's on, it doesnt work. Do I need to refresh it for all until now registered users somehow or?
It's not a bug, its how vB is built. If you opted not to save sent messages in the beginning in the main options, then it sets the default for users when they register to not save sent messages. If you decide to go back and change it so you want to save your sent messages in the main options, that applies to the users that register from now on. You can ALWAYS still change it in your UserCP if you want to save your sent messages or not