Node weight always changes to minimum when/after editing a node

Hey guys,

I noticed a bug of weights:

Whenever I try to save a node with the weight 0 it gets changed to -20 (the minimum). So if I want to edit this node, -20 is selected as the minimum value. So, in order to not destroy my sorting, I have to change it manually back to 0, so it appears at the same place as it was before. After I saved the node, it gets -20 back again ....

I don't get the point, why it doesn't save the 0 value, so I can set positive values for other nodes which should come on top, and negative values to get a lower rank. 0 should be the default and some kind of "neutral" setting.

I appreciate every help.

Thanks in advance
Jonas

Content type settings of weight:

Enable
 -Yes

Weight Range
 ± 20

Use Menu Weight
 -No

Default Weight
0

Sync translations
 -No