After a lot of trial and errors I took a closer look at the OpenOfficeBase interface. I was sure nothing was wrong with my statement so there must be something in Base that I'm missing.
In the toolbar there's a button with SQL and a checkmark which says "Execute SQL-command immediatly". Thought it wouldn't do any harm if I enabled it and gave it a try. And there it was, my query with date filter! I have no idea why that button is there or what it's exact function is, but enabling it made my query work.
Thanks anyway for the suggestions, but apparently we've got to look further than just the language ;-)