I have Linux Mint Debian Edition (based on Debian 8.5 64-bit) and Chromium v53.0.2785.89.
No extensions enabled.
Since last week or of about 2 weeks I have this problem:
When I open edit mode of any task:
1. It opens normally
2. In ~0.5 sec setup options are disappearing, so I have empty blank of everything at this mode of selected task. But all settings are available by blind clicking.
At Firefox it's ok (there is not this bug)
Video opened by VLC: http://rgho.st/64y4dKy4S (better to download to watch without artifacts)

I don't want to use FF, but Chromium :)
Maybe you can solve this issue or you have any ready solutions of this problem?