If I open a .psd file, remove the alpha channel, resize via 'Image Size', and then create a new alpha channel, the newly saved file won't respect the alpha channel anymore. It's as though resizing it breaks any ability for me to save an alpha channel, no matter what I try.
Here's an example .psd file with the issue — http://we.tl/SOsNqsc7XW — it doesn't display transparency when opened in external software (Preview for example) but in Photoshop the Alpha channel appears to all be setup correctly. Can anyone confirm to me, or tell me what I did wrong?
I forgot that if the sum of the image layers has even a tiny part of transparency in it, it will use that for transparency information instead of the alpha channel. In this case, due to the resizing, the background layer must have had a slightly transparent pixel somewhere on the edge. Refilling the entire bg layer properly did it. :)