ChromeOS:
73.0.3673.0(Platform 11625.0.0-19.01.21) kevin test
Input tools version: 73.0.20181227.227100664

Steps:
1.Switch to UK keyboard.
2.Switch to A11y.
3.Click 'AltGr' to open AltGr layout.
4.Click on '¨' (or '˛')key of the top line.
5.Repeat steps#3-4 again.

Actual:
3.1 Nothing is inputted, keyboard goes back to main layout.
4.1 '¨' (or '˛') is inputted, then keyboard goes back to main layout.