Search year permit expiry before single permit is approved

Hi, I also posted this on the single permit thread, but I think this might be a more appropriate place to ask.

I am currently on the search year permit with unlimited work rights, which expires at the end of October. I am applying for a 5 month traineeship with an EU institution, which could potentially start before my search year permit ends, and for which I would need to apply for a trainee single permit to cover the remainder of the traineeship.

The point of the search year is supposed to be so that you can start working immediately while your single permit application is processed, but as I am coming towards the end of the validity of my search year permit, my question is what happens if I start working and my search year permit expires before I receive a decision on the trainee permit application? Would I need to stop working and/or leave Belgium, or is it similar to the Annex 15 situation during the transition from student permit to search year, where you retain your work and residence rights while the application is being processed?

Grateful for any advice on this, if anyone has been through the process before or is currently going through it.