There method isUacOn() has:
if (IsPlatformWindowsVista) {
where it ment to have:
if (IsPlatformWindowsVista()) {

The result of the broken code is always true, so we think non admin users on XP can elevate using UAC and allow DT to try to install java, and JCP to try to run ssvagent to change between new and old plugin.
In both these cases the run will fail with an appropriate dialog, but the expected behavior in JCP is that the option is grayed out, and in DT is that the failure dialog saying you don't have the privileges to do this is shown.

IsUacOn is in both deploy/src/plugin/win32/toolkit/common/privileges.cpp (for DT) and in deploy/src/common/windows/native/Platform.cpp (for JCP).