javascript - Odd IE9/7 style issue -

so baffled , hoping can give me ideas try. not sure details include let me know if dont describe enough , i'll add more.

we inherited .net mvc 4 app former company has version on our clients production server. recently, after few updates us, our client noticed of menu items, styling, etc screwed on test , qa servers in ie9 works on production (production still previous companies publish). test , qa versions work fine in ff , chrome

using ietester , ie11, tried viewing page in ie9 mode did not see same issues client having, tried older versions out of curiosity. managed reproduce issue, in ie7 not ie9. had client verify in fact using ie9 , is.

i did compare older versions of our _layout.cshtml , there isnt single thing changed other favico entry. far can tell, havent changed css or styling.

i have webex meeting client tomorrow @ ie see if can find anything, can give me ideas of cause this? particularly page works in ie9 not his?

sometimes when set default browser mode ie7 , document mode ie9 standard , try again change browser mode ie9 compat view unfortunately browser version detected ie7 , solution problem change browser mode ie9 not ie9 compat view browser version detected ie9