This video from the USA says about itself:
Tufted Titmouse Rescue
7 April 2016
Tufted Titmouse gets hopelessly stuck inside a bird feeder and makes bird noises you only hear under extreme stress. Fortunately I was around to notice. It appears the titmouse was trying to reach a choice seed way inside the feeder and its crest laid down going in, but then popped back up and acted as a very good fastener to make it impossible for it to ever get out.
Upon reflecting on this it appears to be a design flaw for a small bird feeder if you let the level of food get below the window openings the seed no longer flows to the feeder port tempting the little ones to try and squeeze in after the seed. It’s an otherwise great feeder but it could be left unattended for a long time – safe as long as you keep a lot of seed in it.