Aperture shifts in expo override

[IDflash]

When recording with my t3i with expo. override switched on it randomly happens that the camera switches the aperture to a very low point just to switch it back again after a short time. In the video attached you can see this effect. It isn't connected to shutter speed or aperture as it happens in all different settings of those two.

https://www.dropbox.com/s/ybwi3hv4g2eaaa9/Test.mp4?dl=0

Version: Nightly.2016Jun13.600D102
RAW video - (MLV) - Off
Raw video - Off
WB - Auto
ISO - 100
Shutter - 50th
Aperture - 7.2
Exp Lock - Off
Exp Preses - Off
Exp Override - On

[Walter Schulz]

There should be a warning displayed after switching to movie mode:
===
!!!  Auto exposure !!!
Set 'Movie Exposure -> Manual' from Canon menu
===

It's only visible for about a second.
@a1ex: Can we make sure message will be displayed lot longer. 5 secs?