I don't believe so. At least I can't see any light under mine when opened or closed. It may be that a seal just needs to be adjusted....of course, it might be normal and I just haven't seen it ( I'm fairly new to slide outs myself ). Are you referring to the entire underside of the slide or just the font corner?
2012 Chevy Tahoe LTZ - HD tow package
2017 Rockwood 2703WS Emerald Edition