Issue
The installer from https://minecraft.net/download does not appear to detect my existing Minecraft install after being run. I expected it to show me the options to Change, Remove, or Repair the install. Instead, however, it only gave me the option to install. The install path it picked by default is where the game is already installed at. The image dfdSkBeU shows the interface I get when I run the installer (despite Minecraft being installed already), whereas image 8lp85tA is the interface I was expecting.
Install history
I didn't do a clean install of the game after the new launcher rolled out, and instead let it automatically update. It updated to the new launcher without issue by the 100% roll out milestone.
Extra info
The launcher and game works perfectly fine otherwise. I get the correct installer interface (with "Change, Repair, Remove") on a Windows 10 64bit machine that underwent the same auto-update process, and a clean install confirms that the minimal interface is shown ("Install" at given path).
Minecraft shows up in the Control Panel -> Programs -> Programs and Feature interface on the affected computer, version 1.0.0.0 installed on 2014-12-23 with size 1.22MB.
MD5 sum of my MinecraftInstaller.msi
C:\Users\tfd\Downloads>certUtil -hashfile "MinecraftInstaller (4).msi" MD5
MD5 hash of file MinecraftInstaller (4).msi:
16 d3 f9 4b a8 d3 8a 21 2e f9 22 77 40 47 54 ec
CertUtil: -hashfile command completed successfully.
Setting to community concensus as 2 users had the same issue on IRC, one of them was fixed by running adwcleaner to get rid of relevantknoweldge(not sure if related)