Maybe the anti dust mesh is not lined up correctly...which means every time you install an new camera even though it's working it's being cancels because it's not aligned in the phone correctly..what I would do is take the screen out and take the camera and earpiece out and check and see if you could see both holes one being small and one being bit larger.
Loca glue is messy unless your buying them in sheet form then applied by machine...if you don't want glue in the backlight just remove it off the back before glueing but keep in mind it is vey delicate and in some cases people just resolder a new one.i used to do refurbishing and if you have the machines and you know the proper way to fix with no esd or particles then you can make some money.
My understanding is that if you pull the LCD connector before disconnecting the battery, that creates a sudden drop in voltage which will correspond to a sudden increase in amperage which blows the filter. I know that you mentioned that you didn't have the iPad powered on, but in the work of removing the screen, you may have pressed the power button at some point?
Sounds like you damage the proximity sensor which is the front facing camera and it also has a mic which can be easily damage if your not careful I would try replacing and seeing if this fixes your problem