You cannot remove from view statuses that are used in the workflow.

yes of course but as you see I do not use status OPEN

What is sort order of first 3 statuses ?

I thnk ambiguity is that sort order is the same for "Open (PROD)" and "Open"

I changed sort of statuses and in result my workflow goes crazy... I have to create it again. Seems you use --in composition of workflow-- sort order but not ID of status.

If I have right changing sort order on statuses demage existing workflows definition.

Good point is you had right... seems now filtration window of workflow allows to turn off more items... When I fix my workflow I will test this again.

Seems you use --in composition of workflow-- sort order but not ID of status.

Yes, of course.
Postion of status on the workflow should not depend on creation order, but in the order you expect it to be.

Let me explain problems I think in other way.

I have statuses defined like this:

I have empty workflow:

I would like to hide all status (on workflow definition page) and keep only Draft, T1, T2
To do this I open filtration dialogue:

and... most of statuses cannot be unchecked.
I can only UNCHECK: T1, T2

So my question is why I cannot hide on the view statuses like OPEN, QUALIFICATION etc. ?

Hi,
I has a look at the code, and code locks status only if it is used in the workflow.
The only possibiliy I can imagine, is that these statuses are used and linked to a status you just don't see (because it is idle).
I just tested, this case leads to what you face.