If you want to go a little more in depth and fix this more or less permanently, it's quite easy. There are 3 screws under covers on the back. Then the two pieces can be gently separated, they are held together by two clips. I turn was able to defeat the lock mechanism by looping a zip tie through a hole that now holds it in the 'unlock' position.
This took me about 5 minutes. It now works like any stick blender should!