Dolphin seems to have some peculiarities about what images and what folder locations that it will allow you to enter into those fields, and I haven't managed to figure out the strange logic of it all. I would recommend saving the image you want to use for both of these as both image names and upload to your template folders.
For ex. if you want to use the default bx_profile.png: 1. save the image to your desktop and rename it dashboard.png. 2. upload the new image named dashboard.png to the folder see more /templates/YOURTEMPLATE/images/icons/. 3. clear your cache and reload your browser.
The image should now show up in all instances as the same for both categories.
For ex. if you want to use the default bx_profile.png: 1. save the image to your desktop and rename it dashboard.png. 2. upload the new image named dashboard.png to the folder see more