exp collectors loses collected exp when exiting, save&exit doesn't preserve it either.
Yeah, I never implemented a save for experience siphons in the prototype version. The next version that is coming out is way more polished as I didn't leave anything out and has way more stuff like 10 dimensions, 20 biomes, +2000 items, etc... It will be the first non-prototype release. 1.47 & 1.48 was to see if people liked the game style.
Thanks for reporting bugs as it makes it way easier to fix them.