I just found that there is no "local history" for .xsl file. When I tried to "Compare With-->Local History", nothing would happen. Anybody has any clue?
I tried this on 5.1 and 5.1.1 on different PCs. .java and .xml files are all fine.
PS. 1) the file is small(50K)
2) the file was changed several times today
3) the pref is default <7 days/50 entries/1M>