The problem lies with the semicolon character itself. It is the default SQL delimiter. Although it seems to work through the CLI as a password, the .NET provider (which Toad uses) is having a problem with it. The later DB2 clients are throwing an exception within the DB2 Provider itself. It appears this may be an IBM .NET Provider issue.
解决办法
Change the password, so it does include a semicolon. Other special character, like exclamation points for example, work fine. The error seems to be isolated to the semicolon character only.