Files repaired on Modify

I'm seeing some behaviour I don't understand. If you modify an installation, but don't actually add
or remove any features, then I thought nothing happened. If I delete a folder before the modify,
then the installer repairs it. I'm not seeing anything in the log thought that indicates why this is
happening. During ProcessComponents it seems to identify the missing files, like so:

Action 07:52:09: ProcessComponents. Updating component registration
MSI (s) (24:B8) [07:52:09:384]: Executing op: ProgressTotal(Total=10,Type=1,ByteEquivalent=24000 )
MSI (s) (24:B8) [07:52:09:384]: Executing op:
ComponentRegister(ComponentId={7D81B708-071A-4183-84D2-729868B60F72},KeyPath=<path-to-my-deleted-file>,State=3,,Disk=1,SharedDllRefCount=0,BinaryTy pe=0)
1: {C96A5806-5732-4752-8CD1-62F7C43D3BD4} 2: {7D81B708-071A-4183-84D2-729868B60F72} 3:
<path-to-my-deleted-file>

and then later on I see this:

MSI (s) (24:B8) [07:52:09:765]: Executing op:
FileCopy(SourceName=<my-deleted-filename>,SourceCabKey=<my-deleted-filename>,DestName=<my-deleted-filename>,Attributes=512,FileSize=195072,PerTick=3 2768,,VerifyMedia=1,,,,,CheckCRC=0,Version=1.8.7.1 10,Language=2057,InstallMode=58982400,,,,,,,)
MSI (s) (24:B8) [07:52:09:765]: File: <path-to-my-deleted-file>; To be installed; Won't patch; No
existing file
MSI (s) (24:B8) [07:52:09:765]: Source for file '<my-deleted-filename>' is compressed
InstallFiles: File: vsibuild.exe, Directory: <my-deleted-folder>, Size: 195072
MSI (s) (24:B8) [07:52:09:765]: Note: 1: 2318 2: <path-to-my-deleted-file>

How would I detect that the installer is actually doing something? I have conditons based on a
feature being installed (&feature=3), a feature being removed (&feature=2) and a feature being
repaired (REINSTALL >< "feature"). This all works pretty well, but not for this instance. Would I
have to have conditions based on the components instead?

Any ideas?

Thanks,
Rob