> of course elog should remember the choice, so it will be possible to expand
> N threads over the M total ones..

How should elog remember that? If you put this into the URL like

http://<elog-host>/<logbook>/?exp=12&exp=14&exp=18

to expand the entries 12, 14 and 18, it might work fine. But imagine that some uses
have very long list with thousands of entries. This would make the URL very long,
everything very slow and could even crash some browsers.

What I usually do is to not expand the list. If I click on an individual entry, I
see then the expanded thread for that entry above that entry. But you probably
realized this possibility already.