At our project we use Granite fileupload widget ('granite/ui/components/foundation/form/fileupload') to work with images and videos. To specify the family of assets supported to upload we use configuration's property 'mimeTypes' that is simply passes on the value to 'accept' attribute of 'input' html tag.
We use regexp as the attribute's value (say, image/.* -- HTML input accept Attribute) and it works fine for the first time, however when a user simply opens dialog again the validation blocks the dialog from submitting because it thinks that the field of the asset is empty when it's 100% still there. If we change the property to 'image' value -- everything works great.
Checked with the cust care team. The Response was:
Recently there have been a lot of issues reported against 'granite/ui/components/foundation/form/fileupload'. Customer can open a Daycare ticket with detailed steps on how to reproduce along with component they are using so the team can investigate further and validate.