Currently, private messages are handled with the same syntax as the channel messages. That means that the source for private messages is set to the bot's nick.
In-depth explanation:
Syntax for messages: realSource!~realSource@foo.bar.com PRIVMSG #channel :!command
Source: #channel (correct)
Syntax for PMs: realSource!~realSource@foo.bar.com PRIVMSG botNick :!command
Source: botNick (incorrect. realSource is the actual source here)
Currently, private messages are handled with the same syntax as the channel messages. That means that the source for private messages is set to the bot's nick.
In-depth explanation: