Wrong filenames in IE

When downloading photos in IE I get another file names .jpg then real. For example I get sometimes main.jpg and sometimes even =_UTF-8_B_MDZfcGVzYXJvMDcuanBn_=.jpg instead of real 06_pesaro07.jpg file. The problem is only in IE . The Firefox gives real correct names.(both 6.0 and 7.0 versions)
Can anybody explain this strange thing?
Thx, Alex