Hi,
I tried re-installing, no luck. Restoring my tasks worked perfectly.
On your hint for a task killer app, I started looking to other apps which might have been conflicting.
I couldn't find an app with such purpose, so on a hunch I disabled the default HTC power saver. Then when I started tasker, it crashed (crashlog is submitted through the play store), second time starting tasker, it lost all my tasks, which I luckily had backed-up for the re-install, after recovering the tasks, tasker's background service restarted!
I also reactivated the power saver, but the background service keeps running... ? So I'm not really sure if that was the problem.
Anyway, thanks for your help :D
-- Daan