Broken drag-n-drop in Flatpak build

Flatpak build of Gajim does nothing when the file is drag-n-dropped inside chat window. You can see "drop files or contacts" message upon dragging, but dropping does nothing. Nothing reported in the console, even with --loglevel=DEBUG.

Versions

OS: Fedora 33
Gajim version: 1.2.2 (Flatpak commit 14ca2df70126662668f45c0785f1faa6ab690a920ef8bc02623bf213ad02cc32)
GTK version: 3.24.23
Python-nbxmpp version: 1.0.2

Steps to reproduce the problem

Open chat window
Drag-n-drop any file to the chat window

Expected behavior

The file is sent

Actual behavior

Nothing happens, the file is not uploaded.