The email templates included with the scheduler will send a user to the login page if they are not already authenticated (obviously), but will not redirect to the issue page after logging in.
I have fixed this issue. The URL in IssueLink.en-GB now reads:
<%=Data.GeminiURL%>Default.aspx?ReturnUrl=%3Fp=<%=Data.ProjectID%>%26i=<%=Data.Issue.IssueID%>
Note the use of ReturnUrl and the hex characters instead of & and ? (%3F and %26). Also note that I replaced the link URL in both html\IssueLink.en-GB and in text\IssueLink.en-GB.
May I suggest that this make its way into the next version of the scheduler download?