Is rest length < 1 a problem?

Hi. 

I have experienced some different problems when the rest length of my springs become less than 1. Sometimes problems can be somewhat solved by changing bending strength of other numericals. But I am not really sure why this happens? 

if the rest length is less than their start length they want to get smaller, if it is zero, the springs will minimize. But if i have lines of 0.5mm and the same rest length? Should that be a problem?

Cheers Rasmus