It is only under XFCE so.

(In reply to Hanisch from comment #1)
 It is only under LXQt so.

XFCE, LXQt or both?

Only under LXQt. But it is impossible to setup any settings.

Confirmed with LXQt. Behaviour is the same as
>su -c 'dbus-launch krusader'

This does not reset the environment variables, specially
>XDG_CONFIG_HOME
>XDG_DATA_HOME
.

Question is: why is it different for plasma and e.g. LXQt?

Note for myself: 
>su -c "KDE_SESSION_VERSION=5 KDE_FULL_SESSION=true dbus-launch krusader"
>su -c "HOME=$HOME dbus-launch krusader"
does not change anything.

Note for you guys:
>su -l -c "export DISPLAY=:0 && dbus-launch krusader"

will launch Krusader with root settings. However, the command for the "Start root mode Krusader" action is (and should be) hard-coded. I'm still unsure if the current behaviour is a "feature" or an unwanted bug - it's a matter of taste imo.

*** Bug 162417 has been marked as a duplicate of this bug. ***

There is another report #162417, which complains that root-mode krusader DOES NOT use settings from current user (actually written by me, but up-voted by other users). I actually can't find any use-case when user needs different settings for root-mode (so why to bother with configuring krusader twice?; and if several users share the same PC, even configuring krusader twice may not help — because different users may want different settings, but all of them may user root-mode from time to time).

Anyway — this seems to be platform-specific — but neither behavior satisfies all users — so it should turn into platform-independent, but CONFIGURABLE — so that "start root-mode Krusader" menu items does what the current chooses (not just silently uses current-user or root-user home dir).

I write here, because somebody marked bug 162417 as duplicate of this one.

Ideal solution (as for me) is the following:
  * user clicks "start root-mode krusader" in the menu;
  * the current instance of krusader, before launching anything, first looks for a special flag in the current user settings: "Do the current user likes the root-mode krusader to use the same settings or settings from the root user?" (as for me, the first should be default — but I don't insist on that, because opinions may vary);
  * depending on the value of that flag in current-user settings, the current instance of krusader launches a new root-mode instance of krusader either in a way that it continues to use current user settings, or in a way that in uses settings from the root user;
  * (this behavior should be platform-independent; i.e. whether root-mode krusader uses current user settings or root user settings should depend on a value of the flag in the current user settings — not on the platform; I believe that every platform allows both ways)
  * (this requires a new flag to be introduced into user settings)
  * (additionally, root-mode krusader, when it uses non-root-user settings, may need to be careful not to overwrite user settings with wrong rights (i.e. to create files in user's config dir owned not by root, but by the inherited user) — if needed to create something — but it may be a matter of a separate bug-report if such case arises)