You're probably just seeing things, but there is a way to test your theory assuming you're on PC.
Every weapon has a .dat file that determines its appearance. Each weapon even has a unique .dat depending on race. For example, mandau for Hume Male is found under ROM\136\102.dat, but for Mithra, it is file ROM\138\91.dat. If two items have the same appearance, then the same .dat file is used for each piece.
This means if lv95 Mandau is bigger or brighter or different in any way from the lv90 or even lv75 Mandau, then it will use a different .dat file. If you replace the lv75 mandau .dat file with a bronze dagger .dat file and your lv95 Mandau will remains unaffected, this will suggest that your new dagger is, in fact, somehow different in appearance.
You could just find out if there is a lv95 mandau .dat file, but I don't have any current .dat file lists and I'm too lazy to check for one myself.
Edited, Feb 6th 2013 10:45pm by xypin