Why is Lightroom changing file names when exporting? How I can I stop it?

Ok.. So I am still new to LR CC & 6 but have used 2.7 for a while now. I just noticed that when I am exporting jpegs (to a new folder inside the original folder) LR adds an under score "_" at the end of each file now. I have the existing file option set "as overwrite w/o warning" but have also tried "ask what to do"  (but LR is creating the folder anyway so there aren't any duplicates). This doesn't happen in 2.7 and I would really like to figure out how to stop it from doing this, since I use these adjusted jpegs to overwrite the originals and now I can't just move them into the original folder since they are now all different. I am a printer and use LR a lot to re-size images in bulk so they load faster in other programs (I don't need the larger files for quality). Any help would be appreciated!