I found a possible reason why the (well known) admin loop might occur. An other problem is that changes to the general settings are NOT saved into the db either

The anoyance is that --when logged in as adminuser-- a click on the "administration menu" causes a loop to enter that only shows "This is your first time to enter the administration section."

Several solutions posted around here go from disabling the firewall (absurd) to modding the code (even more absurd), or changing browser (totaly nuts)

My problem started when adding a custom theme to the directory ./xoops_path/themes/

SOLLUTION:
If you have the loop problem, then first check next things:
- the new theme directory AND its files inside MUST have public read access (typicaly chmod 755)

- make sure ALL needed files are in that theme !!!!
if even 1 gif file is missing, the loop problem will start.
read other documentation on how to make your own themes if needed.

advisable is to move any added themes to a different location on disk and test one at a time, so you know which theme is causing the trouble

As said at start, this might be only 1 of the possible scenarios that causes the loop to start.
good luck ...

I've been changing the templates and some modules to fit my needs (small html changes).

After some time I realy got fustrated since XOOPS keeps cache of the site at several levels, making it difficult to manage (delete)/ rebuild them.

So doing some experiments to see how my html changes looked at frontend, i've started with this procedures to clean of purge the cache:

1) empty folder xoopsroot/templates_c/ (has some effect, if empty, cachefiles are rebuild right away )
2) backup and empty db-table tpl_source (very efficient lol, all is gone now)

during stage 2 i've lost my site, putting the backup back doesnt make a difference :-/ so how do I force XOOPS to rebuild the tplsource in db again so it contains a recent "build" of my templates, htmlfiles etc.... ??

Yeah, we definitly need such feature. Especialy to build modules that take those fields in their templates too, like
and offcourse to write back in those fields too