Fabia mk1 estate load cover not retracting. Any experience?

My load cover has ceased to work properly in the boot of my Fabia.

I have it out and tried to manually roll it back up, but the mechanism just spits the rolled up cover back out. How rude.

I have taken the one side apart (the near side if you were looking at one fitted to the car) to get the cover and mechanism out, nothing seems obviously broken but can't see how to re-tension it.

Anyone had any experience?