Sorry for that. Here is video sample. First resize is with mouse and shift-ctrl, second is vith keyboard and shift+ctrl+ arrow down.
https://www.youtube.com/watch?v=P7MC9BPYnaM
as you can see, it tries to resize target proportionally, but calculations are wrong from some point when target becomes smaller.
System used is Xubuntu with XFCE 4.12, java version "1.8.0_121" Java(TM) SE Runtime Environment build 1.8.0_121-b13
From reddit: