Auto switching stops working after cmd line

[timsofteng]

Steps to reproduce

1. Select insert mode.
2. Change lang to non English one, let's say jp.
3. Exit from insert mode to normal mode (works here, lang now is english).
4. Select cmd mode with :.
5. Exit from cmd mode to normal mode with Esc.
6. Select insert mode.

Want Lang switches to back to jp.

Got Lang is English.

UPD The same story with search with / insted of cmd line.