Lotus Notes want to capture date/time FIRST time a field changes status

I have reviewed posts and can't find exactly what I am looking for.

In a form, I have a field called Status. It has values
Not Started
Working
Held
Approved
Complete

An end user wants me to capture the 1st date the status is Working, Held, etc.  (any status other than "Not Started"). These fields have to be separate fields so I can include in views for her.

I set up 4 hidden date fields - Capture_Working, Capture_Held, etc.

For each one I used this formula language for the field value (this example is for Working status)
@If(@IsNewDoc; "";
@If(@IsDocBeingSaved & Status = "Working" & Capture_Working = "";@Now;Capture_Working))

Held would be Capture_Held:
@If(@IsNewDoc; "";
@If(@IsDocBeingSaved & Status = "Held" & Capture_Held = "";@Now;Capture_Held))

So I thought a new form would have blanks for all of these date fields. It did.

I then changed the status to "Working" and sure enough, it captured the working date/time. BUT it also populated the other capture dates. I don't see how it did this?

A few minutes later I re-saved the document to be sure the Capture_Working field did not change; it did not.

Can you help me figure out why the other capture date fields are changing? I don't want them to until the status actually changes to the status they are referring to.