when I tried exporting a with multiple layers to PNG and then to TIFF, I had the same problem: all the layers, including the partially transparent ones, exported as 100%, as far as I could tell, resulting in a darker and "heavier"-looking image. I did not have this problem when I exported to a PDF, however. I thought that had to o with the difference between lossless versus lossy formats (I would rather have used the lossless formats).
I can't remember if I had tried just merging all the layers or even if I already had.
can anyone tell me how if they know of this problem and what to do about it?