You have a computer A with amarok 2.6 inside
You have a computer B
you copy you whole $HOME from A to B
You install amarok 2.6 onto B
You fire up amarok 2.6 on B
It search for a new collection with brand new settings(not the same sets of file etc) and as always by rebuilding its collection it looses id3tags, playlist saved in the interanl db etc...

Why does it have to be like that?

Are both computers using the same distribution?
Different distributions have the name of the KDE local settings folder - which may be causing this.

Yes both are KDE 4.9 Kubuntu 12.04 32 bit
The problem occur when I am using amarok installed from sudo apt-get install amarok

When I compiled the git version of amarok on B it works fine... I seem always to have more problem with the packaged version rather than with git one

The versions of Amarok installed on both machines must be the same (or the version on machine B must be newer if you will not be migrating it back to machine A).

They were exactly the same since installed from package manager..

Correction: after moving back from B to A again with amarok version on A >= B it still will not found the collection (full rescan and it will found 69 track....)

From my experience, should it be id3 tag album cover, playlist, anything, i have never seen a feature related to the collection hadnling that is working properly in amarok...