Yes, the plugin needs to be updated for 1.4. However, as far as the complaint about being confirmed before receiving a PM - Why would you want to be left in the conversation unless you have intentions on replying to them if they reply to the welcome conversation? I just have my settings where I automatically leave the conversation once it's sent to the new user, and within my message - I link them to the support section if they have any questions.
Nonetheless, this plugin is excellent. I want to see something how they have on vBulletin, where it automatically posts in a set forum when a new user posts. Example, if someone posted a new thread in the Introductions and Farewell forum, it'll post in it right away with whatever content you have in it (Eg. Welcome to xenForo Forums! etc etc).