I found that Opus 9 is case sensitive for the file icon.
Give an example, for the PDF file type, first, I use foxit (pdf reader software) to read pdf file and all the pdf file icon is 'foxit icon'. Then I installed acrobat 8 to read pdf file and set acrobat as the default reader for pdf file. Then I found all the 'PDF' extention file's icon is 'acrobat icon' but all the 'pdf' extention file's icon is still 'foxit icon'.
It it occured in Opus 9. However in Window Explorer, 'pdf' and 'PDF' extention file has the same icon which comes from acrobat.
I think maybe it is a mirror bug.