Multiple subform with a document inside fails

You can find a reproducer project attached to the issue. The form that start the task (without the document field) works fine, the first HT that has a multiple form with the document fails. --------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Add DocSample project from the attachment to some repository in .niogit. 2. Open the project in Authoring and navigate to emea_ssa > docsample. 3. Open the DocProc process and in the "Insert" activity add the group of the current user to "Groups" (in order to see the generated task). Save. 4. Build & Deploy the project. 5. In Process Definitions start the DocProc process and fill in some random data into the form (from example those from the attached picture). Submit. 6. Claim the task and try to upload some document to the file. Expected result: Form layout stays unchanged, the document is uploaded. Actual result: See the attached picture.