Newsflash:

After downgrading libxml2 and therefore getting my desktop back, i left the widgets unloaded after the reboot and tried another alarm. Nothing, silent popup as ever.

Next, i restored my widgets and did another one-off - nope, nada.

Okee...

Now, i used alarmed to create a one-off, and guess what - that one gave me sound!
Curious, i created another one in Clock / alarmui - and got sound too!
Just to confirm, the next one in alarm-ui was a repeating on. And for the 3rd time in sequence, an alarm sounded.

So, can anyone explain this behavior?

EDIT: also heard an alarm tone this morning, good. Let's see how long (for how many days) this is bound to happen...