Groupselect not working < 2?

I've got a funny phenomenom when using groupselect.
This is (a part of) the code I use to filter:
{joodb groupselect|car_brand|2|true}
{joodb groupselect|model_en|2|true}
{joodb groupselect|built_from|2|true}
{joodb groupselect|engine|2|true}
{joodb groupselect|fuel_en|2|true}
This works...

When I change them into
{joodb groupselect|car_brand|0|true}
{joodb groupselect|model_en|0|true}
{joodb groupselect|built_from|0|true}
{joodb groupselect|engine|0|true}
{joodb groupselect|fuel_en|0|true}
...so I can use them as pull-down menu they don't "communicate" any longer and they always show all values and the result stays empty.

Any ideas? :-)

Tried to but isn't working as
{joodb groupselect|car_brand|1|true}
{joodb groupselect|model_en|1|true}
{joodb groupselect|built_from|1|true}
{joodb groupselect|engine|1|true}
{joodb groupselect|fuel_en|1|true}
either...

Is there an explanation for this?

Did you get an answer to this? I have the same issue

It's working, what happened I don't know. I didn't change a thing before I noticed this, funny but I'm glad it's working now...

thanks for comming back ;-)