It's an unfortunate situation, but there simply isn't an exhaustive list of all the bugs in the original script compiler out there. The original engine uses the bytecode, so these mods work mostly okay until they're used with OpenMW, which uses the script source instead.
Occasionally, simply due to blind luck, this happened to guess the behaviour the mod author wanted, and they'd release a mod with correct bytecode but script source that really shouldn't have produced that bytecode.
The mod is supposed to be broken in the original engine, too, but instead of spitting out an error when something's obviously broken, the original CS just picked whatever batshit crazy bonkers thing based on unpredictable things like what colour socks Todd Howard was wearing on the day the script was compiled.
