I don't think I should post it as bug, because it seems I miss something.

When I run select "Suspend" or run in konsole the following command, I only get my screen locked by screensaver. And the computer doesn't suspend.

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qdbus org.kde.Solid.PowerManagement /org/kde/Solid/PowerManagement/Actions/SuspendSession suspendToRam

However, these commands:

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pm-suspend

and

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qdbus --system org.freedesktop.login1 /org/freedesktop/login1 org.freedesktop.login1.Manager.Suspend true

work as expected. I.e. I can suspend from command line (or using hotkey if I make it run this command), but I cannot make computer suspend using KDE.

KDE 4.11.0 in Kubuntu 13.10.
I suppose there are Solid's logs somewhere, but I couldn't find them

What is the output of "upower -d", in particular the last section under the title "Daemon:"?

I get the following:

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$ upower -d
...
Daemon:
  daemon-version:  0.9.21
  can-suspend:     yes
  can-hibernate:   no
  on-battery:      no
  on-low-battery:  no
  lid-is-closed:   yes
  lid-is-present:  yes
  is-docked:       yes

It seems one of the latest updates of kubuntu fixed this problem.
During installing updates, my computer suddenly went to suspend mode. I switched it on back. Then I saw message about "kded4" crash.
And after this going to suspend using kde works fine.

Okay. The output you posted definitely indicated that UPower believed your system was not capable of suspending - and that the lid was closed. It was likely this condition that caused KDE to immediately suspend your system when it became possible to (as a result of the updates).

Topic marked as solved.

No, finally it doesn't suspend again after system reboot. Seems that crash of kded4 did something for a short time, but the problem persists.

UPower believed your system was not capable of suspending

No, there was "can-suspend: yes". It showed it can suspend.

And yes, the lid was closed: I'm using dock-station and my notebook is closed.

Oops. I transposed the lines.
What is the output of this command?

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qdbus org.kde.kded /org/freedesktop/PowerManagement CanSuspend

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$ qdbus org.kde.kded /org/freedesktop/PowerManagement CanSuspend                                                       
true

Does the following command cause your system to suspend?

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qdbus org.kde.kded /org/freedesktop/PowerManagement Suspend

No, it doesn't. It only starts screensaver

Okay - that is the real cause of the issue. Your system is not entering suspend mode when KDE requests it to.
Do you see a process called "polkit-kde-authentication-agent-1" running on your system (or any other process with polkit in the name)?

I have the following running processes with 'polkit' in name:

/usr/lib/policykit-1/polkitd
/usr/lib/kde4/libexec/polkit-kde-authentication-agent-1

What is output if you run the following command?

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dbus-send --system --print-reply --dest="org.freedesktop.UPower" /org/freedesktop/UPower org.freedesktop.UPower.Suspend

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$ dbus-send --system --print-reply --dest="org.freedesktop.UPower" /org/freedesktop/UPower org.freedesktop.UPower.Suspend
Error org.freedesktop.UPower.GeneralError: Sleep has already been requested and is pending

This means you have an application which is inhibiting sleep - something which UPower and KDE are both respecting.
Download managers, disc burning applications, etc are likely to inhibit sleep.