Customstring widget misses updated context?

Hi all, I am working on a project where we use a Customstring widget to render buttons (because of styling). For some reason though, the widget's on click microflow does not receive the updated context. It's a simple case: I have a Contact object, with a generalization of Image. I upload an image and click on the Customstring widget which triggers a microflow with nothing more than save Contact and close page. Breakpointing this flow made clear that hasContents remains false even though I've selected an image. What's even more strange is that all the other attributes are saved correctly (Name, Profession, etc). To prove that the widget is faulty in this case: a regular action button with the same flow works fine. Anyone else run into this issue? Is there some knowledge on how to work around/fix this?
1 answers

Why not use CSS classes on a default Mendix action button? In that case you can manipulate everything using that class.