Post one of them, please.
Is there any possibility you have cropped the image from a larger one, and have the [ ] Delete Cropped Pixels option not set (then possibly later resized)? That could leave pixels around the outside of the visible canvas that could possibly influence a final flattened result.
As a thought... You could check for perfect transparency by using the Layer - Layer Mask - From Transparency feature, disable the created mask, then look carefully at the remnant pixels around the edge. If there is any color there other than white you haven't created perfect transparency.
Here's a PNG file I just created with Photoshop CC 2014.1 by erasing around the edges, then a simple File - Save As - PNG format. You can have your Gimp users see if there are any "dirty" pixels in it.
Thanks! I will send this to them to check out, as well as try out your suggestion of layer masking
Thanks for posting an image.
Hm, after looking at your image I'm not sure the problem is in anything you've done.
I did do a Layer Mask from Transparency, and I did see non-white pixels in the RGB channels, BUT... The mask seems to be all pure black (except for the white parts), which implies all the pixels that are supposed to be transparent ARE truly and fully transparent. It also says that my tried and true test of detecting transparency by looking for non-white pixels may no longer be rigorous.
This what i see in gimp
Maybe this is what they talking about, that there is some blue areas that should not be there, yet are after filling in the alpha channel (transparency channel in photoshop)
Same as doing Layer>Layer Mask>From Transparency in photoshop.
Upon opening in gimp
After filling in the alpha (transparency) channel
Which version of photoshop and operating system did you use?
When i tried several different variations in photoshop cc 2014.1, i always had visible pixels that shouldn't have been there after saving as a png
Doing the same in photoshop 6 yielded the expected results of what was there before, was there after saving and no more.
I'm currently using CS6 v13.0.
Im curious what you think is causing the issue here- photoshop? me? gimp? how it's being saved?
As of right now, it seems to be a photoshop issue, going all the way back to photoshop cs3 and still an issue in photoshop cc 2014.1
Anyway, using your posted image as an example.
1. Use Layer>Layer Mask>From Transparency
2. Shift click on the layer mask and check your image for unwanted areas
3. If any found, Ctrl click on the layer mask to load it's selection
4. Delete the layer mask
Hopefully, your image or any other similar kinds of images you make will be okay in gimp and other programs after doing the above.