I edited some pictures to make emojis out of them, removed their background and saved with the original background hidden in the layers. I've done this in the past with no issues, but this time I'm running into a very strange behavior. I've uploaded these pictures on Discord, and in chat it appears transparent, but when downloading the PNG files, the background appears white instead of transparent. What's even more weird is that I brushed it off as Discord bug, and uploaded the pictures on mega.nz, but in mega it shows the preview with the background I removed! Is it somehow able to access the hidden layer after I saved it in PNG?? How can I fix this bug and clean up the files, knowing I didn't keep PSD files?
...As for your second question, when you remove pixels in Photoshop using a mask, it still keeps pixel data. For example if I remove a part of an image
and then run
Layer > Layer Mask > From Transparency and hide the mask you'll notice that all the pixels were restored even though they aren't presented in the original layer:
And when you save PNG24 from Photoshop it keeps all this data (that's one of the reasons why PNGs generated by Photoshop are usually larger than if generated by a different exporter). It's possible that
mega.nz can't show transparency or detected these pixels and shows them.
To get rid of them you could use a different PNG exporter like SuperPNG that has a
clean mask option. Here's an example of generating a layer mask for a PNG exported with SuperPNG with
clean transparency on: