I have clean, updated 19.04 installation and when i switch applications with alt+tab, i get a list of the windows (ie small previews of the actual windows, maybe 300x300) .
When i use shift to go backwards a weird thing happens. I get a second list on top of the first one. This one is smaller (120x120) and has icons, not previews. This new one takes over control until i release shift, or all.
When i release shift first, it switches to the window the second switcher had focused. Also when i release alt+tab first, but then when i release shift last, the old (preview) switcher stays focused. Even weirder, that preview switcher then responds to left and right keys, which it never does otherwise.
I have tried this out on solus which only ever shows the preview switcher and correctly responds to shift for going backwards. So i am assuming this is caused by the ubuntu integrations.
Can anyone confirm this shift effect?