Xml files are extremely slowly reloaded.
I have been using NPP for editing my .bib->.xml library files quite successfully. Easier and faster than the xml editor oxygen. However, with the lastest update some time ago to 7.5.6 (32bit) on win7 I noticed that large xml files, when open while NPP, take unlimitied time to load, while when opened from the explorer with right-click, edit by notepad ++ load minutes faster. There must be something to hinder the files to open. I will gladly sent my files to test. These xml libraries are 800 kb to 1.3 Mb large.
Could be also a plugin. You could test this by starting N++ from command line with parameter
, see http://docs.notepad-plus-plus.org/index.php/Command_Line_Switches.