Lightroom :: Color Labels Lost On Transition From One PC To Another

I started using a mac laptop in the field and always used windows pc at home. A portable hard drive holds the lightroom catalog. It's fat32 formatted so it can be used by both mac and windows.

A catalog made by the mac lightroom opens fine in windows. However, all the color labels are lost. The flags and stars are retained.

If a color label is changed on a photo by the windows version of lightroom, then when that catalog is opened on the mac, that photo has no color label. (even though the mac originally gave it a color label)

And all the original color labels that were made by the mac magically return as they were assigned.
 
To trouble shoot this, I installed the Lightroom 3.6 trial on 2 other pcs - one runs windows 7 32 bit and the other windows 7 64 bit. These installs see the mac created catalog properly.

All the color labels are there and changing one on a windows box is properly reflected on the mac when that catalog is opened.
 
This is so annoying.My main pc must have an allergy to my mac. I removed and reinstalled lightroom on my pc-same problem. Now i have to figure out what is interfering with my main pc lightroom install.

It cant be lightroom cause i removed it and reinstalled it. but it might be one of the plug ins i use. these magically reappearred even after i reinstalled lightroom after removing it.