I just discovered this myself. http://s-witch.cute.or.jp/pants/index.html "They're not panties, so it's not embarrassing!" is the official tagline of the series now. Does this mean that all Strike Witches images should have the 'panties' tag removed?
Not really, but I do wonder if maybe there should be a "not_panties" tag or something similar to reflect this catch phrase since it's so prevalent (there are over 3000 images on pixiv tagged with it). Like yukkuri_shitteitte_ne or kono_lolicon_domome.
She's obviously wearing pantyhose under panties, under another pair of pantyhose, which leaves the panties visible, but not her skin. It's a pantswich on a pantswitch.