In Windows clicking the current window will take you to the previous window.
In WINE clicking the current window will take you to the previous window then jump to the one before that.

Feature introduced in:
Quote

16/08/2007 - mIRC v6.3
...
55.Changed left-click method on treebar items, it takes one click to
open and close windows now.


Code
//window @aaaa | window @cccc | window @dddd | window @eeee


https://www.dropbox.com/s/lxb5jgq8wxz2jjl/mirc-jumping-treebar.mp4?dl=0

Using -nowine does not change the behavior.

I reported this a few years back in WINE.

https://bugs.winehq.org/show_bug.cgi?id=40960