While investigating 7114486, below are the 6ux installer issue I found regarding uninstalling
6ux while 7ux is still on the machine. All are based on install log and inspecting the code.

1) SSVSetup (in RegInstall.cpp)
   It's trying to preload the msvcr71.dll.
   When calling a function in jp2ssv.dll in jdk7, it should preload msvcr100.dll
   or have the function in jp2ssv.dll preload msvvcr100.dll.

    _sntprintf(temp, sizeof(temp) / sizeof(TCHAR), _T("%s\\bin\\msvcr71.dll"), lpszJavaHome);

    HMODULE msvcr71 = ::LoadLibrary(temp);

   We're already doing the correct way in RegFX.cpp.

2) IsDefaultVMInIExplorer (in RegCommon.cpp)

   The function fails and returns early.
   If the function succeeds, there should be the following statement in the install log:

    "-- End in IsDefaultVMInIExplorer --"

   I'm suspecting the incorrect version is used to open the reg key.
   It's likely still using the JRE version instead of the new plugin version starting with 10 for jdk7.

3) StartJQSService (in RegCommon.cpp)

   The following error:

       JQS ERROR: (GetLastError=1060): Cannot find JQS service JavaQuickStarterService


   I think the fix should be check for if the platform is XP before calling InstallJQS() and UninstallJQS().

4) RegJava2IExplorerDefault (in RegCommon.cpp)

   It has an error and returuns early since I didn't see the following in the install log:

       "-- End in RegJava2IExplorerDefault, return TRUE --"

   I believe the checking for the existence of regutils.dll in jre7 causes it to fail.

   We're doing the correct way in our RegCommon.cpp

    if ((_tcscmp(bsMajorVersion, _T("1")) > 0) ||

        (_tcscmp(bsMinorVersion, _T("7" )) >= 0))
    {

        _tcscpy(szRegDLL, _T("deploy.dll"));
    }


Note: problem #2 has been addressed by the fix for 7104732 according to the webrev.