Reader 10.1.2 MUI fails to remove 10.1.0 MUI

So I've created an admin install of 10.1.2 by applying the 10.1.2 patch to the base 10.0.0 msi and it installs successfully on systems without Reader instlled; however, when I try and install it on our systems with an existing 10.1.0 MUI installation, it fails logging that a prior version exists and needs to be removed first.  The REMOVE PREVIOUS property set to YES, so I'm at a loss to understand why this is failing.  While there are language-specific versions of 10.1.0 as MSIs, there's no MUI version of 10.1.0 as an MSI, so I have to work from the base 10.0.0 (right?).  Just for grins I did try patching 10.1.2 onto the MSI created from the admin install of 10.1.0 MUI (originally created by applying the 10.1.0 patch to the 10.0.0 msi), but it doesn't work stating that the patch is for a different version.  I presume this should work, so I must be missing something...what is it?  Thanks!