I know this is super old, but this problem plagued me so I'll answer.
It's obviously not mold, because it can't be killed. It obviously is not hard water/rust because it is sticky resin and not in contact with metal. It is obviously not cigarettes if you don't smoke cigarettes.
The most likely explanation when is that the person who painted the bathroom used general-purpose paint instead of bathroom paint. The moisture is going to cause substances within the paint to separate out. No matter how many times you remove the stains, they will keep coming back, at least until you have scraped all the paint off your ceiling.
A less likely explanation is that honey is seeping through your ceiling from a bee infestation. I wouldn't recommend tasting the orange paint-resin, but that would be a way to exclude honey as a cause.