This question here at DA has a popular suggestion to check
page.tpl.php to see if it says
print $messages;. I verified this and this is the case.
I cleared caches many times, btw after which there actually is a drupal message saying the caches are cleared.
I made sure the
drupal_set_message() functions are nicely outside any conditional statement or php logic whatsoever. I also put all these functions on different places in the
tpl file. Still no result.
The same theme also has another tpl file that I used before and had some commented dpm(); functions that I uncommented but these didn't work anymore either.
Devel module is enabled and I am logged in as admin the whole time.