LR2: TIFF and XMP - not compatible?

I have a few Lightroom 2 catalogs. My main catalog has has "write to XMP" turned on for a while, but just realized my other catalogs did not have this setting checked.

My Canon RAW file directories now get an XMP created when I and change a setting, but I have directories that are scanned film in TIFF format. These do not get an XMP file created. I used the "write data to metafile" function and still no XMP file created.

What's the deal? Are XMP and TIFF not compatible with Lightroom? Is this a flaw in LR2? Or is Lightroom writing the list of setting changes to the TIFF file? (that would be bad - I don't want that - I want to see the list of setting changes if imported again into LR).

Aren't XMP files generated by RAW conversions?

Any TIF I open in LR shows that every setting is at default and Camera calibration is Embedded.

Color me curious here...

But you can do those same conversion adjustment settings to JPGs and TIFFs, though not set the actual WB temperature and tint just an adjustment from "zero". And it's that list of adjustments I want to be able to re-use and back up just like a list of conversion settings for a RAW file.

Why is no XMP being created for my TIFFs?

I think the metadata is written into the actual TIF file (header). Same for .jpg.

Easy to test: Take an unedited tif, crop severely in LR, save metadat, delete, re-import and see wether crop is there. (Or check in ACR if you have that)

Yes, in tifs and jpgs the xmp is in the metadata. Because LR/ACR has no backdoor into the CR2 format (as does DPP) they are forced to write it as a separate file.