Large SXT craft issues!

[The_Beansta]

Hi I just downloaded and installed the latest version of Lack's SXT mod pack, so I could use the new command pods (the entente and osual looked cool), but found that when building large craft, above a certain size, they will glitch out and appear to fall through the ground of Kerbin at ridiculous speeds. The pause menu also doesn't show for some reason when this happens, and nothing works, so game restart is required. Upon reopening the game, and loading the craft in question, the load menu doesn't disappear, and needs to be told to cancel, even though it has already loaded the craft (this only happens when I'm having these issues). The craft size, weight and cost are all set to unknown, and the craft refuses to launch. Also, it appears to be unedditable. This issue is repeatable, and consistent with ALL large craft with SXT pods, and doesn't happen without the SXT pods. Any help would be greatly appreciated, as I really like the SXT pods!

[OrbitalBuzzsaw]

How large?