I work on line drawings of airplanes. Profiles mostly and it seems that when I re-open a file I discover changes made and saved do not appear. In fact I have to re-do an area that was painted no longer has the latest effect. I'm not doing anything fancy or complex - best example: within an area I put in two new lines, save and close. When I re-open the drawing, that change is not there. Or, another example: I open a drawing and there are shadow pixels in an area I painted, saved and closed. All files are saved as PNG.
In the attachment the lines were being changed from black to gray......... all the changes were made.... when I reopened the file the lines were mostly black.
