The way I do it is to generate a log file. The normal way to do this is to use the /L switch on an msiexec command line. This can not be used in this case so you need to set the registry key to generate a logfile.
Open Notepad
Cut the file below
------ Cut below this line ----------------------------
REGEDIT4
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Installer]
"Logging"="iwearucmopv"
------ Cut above this line ----------------------------
Paste into note pad.
Save as SetLogPolicy.Reg
Double click SetLogPolicy.Reg
You may need to reboot I am not sure.
From now on whenever msiexec pops up a log file is recorded in your temp directory. (Your temp directory is found under C:\Documents And Settings\<You>\Local Settings\temp under recent systems and Windows\temp on the older systems) The logfile is given the name MSIxxxxx.log.
Inspecting this log in the first few lines one the parameters will be REINSTALL=YOURFEATURENAME. This will give you some idea to what is being repaired.
Reading logfiles is difficult at first but in the end you will gain a better understanding to how msi works.