When only one resource pack is broken, so only one thing doesn't work right (like a syntax error in the model-format), all resource packs get deselected, when reloading them with F3+T.
It would be better, if only the broken one was deselected and not all, reselecting all resource packs you need is tedious (in one are 3D-Ladders, in another only the font and so on), which could be many.