I'm guessing what I got here is one of Webster's game fixes adapted to 1.4 (several mods say "for 1.4 and 1.5" but they actually crash 1.4 since they include CFG files for ships that 1.4 never had), and since it had to be tweaked to eliminate incompatible 1.5 files I installed manually without JGSME. Apparently that was it though, rafts bob up and down on the surface the way they're supposed to, although during a busy battle I sank a BB and a CV, then went over to look at the debris field a couple minutes later - all the rafts and lifeboats were in the process of sinking.
Not actually a problem since they sank all the way down rather quickly, the trouble I was having was the blasted things hovering with neutral buoyancy where I couldn't see them and they kept setting off torpedoes.
Aside from the one incident of sinking survivors (oh the humanity) the problem looks solved.
