In my new map I came across a wierd bug. If I have gel flinging in the air or being funneled and save the game by logic_autosave or quicksave then often when I get the game reloaded gel doesn't appear only some particles at the loading moment. Anyone knows how to fix it, please ?

Grey.

Unfortunately, there's no way to do that that I know of. Since paint isn't an entity, it doesn't have its position automatically saved.

Try making the dropper drop paint bombs instead, those are entities and should be added to savegame files.