Guix installing different package versions on different machines

[Zelphir Kaltstahl]

Hi Guix users!

I installed Guix on my own machine (Xubuntu 18.04.3) and at work on my
machine (Ubuntu 18.04.3). Although I do `guix pull` and then `guix
package -u`, both machines get different versions of packages installed
this way. I have seen 2 examples of this behavior so far: Emacs (home:
26.1, work: 26.3) and Guile (home: 2.2.4, work: 2.2.6). I don't
understand this behavior, as I thought that both installations of Guix
should use the same repositories, because I installed them the same way
and I even use the same OS at the core. Furthermore I thought, that Guix
installs packages as they have been provided by contributors and does
not perform checks, whether some package is suitable on a system.

Where is my understanding wrong?

What can lead to this behavior?

How can I get the newest versions of all things on all my machines?

Regards,

Zelphir