Workflow condition evaluation not working as expected

First off, let me say the workflow conditions aren't working as I expect them to :-)

Let me paint a picture:

my invoice has 3 lines with 3 different departments (dept1, dept4, dept5 for simplicity sake)

The workflow it gets submitted to has steps and conditions like this:

step1:  If Journal Lines.Department = dept1

step2:  If Journal Lines.Department = dept2

step3:  If Journal Lines.Department = dept3

step4:  If Journal Lines.Department not = dept1

and Journal Lines.Department not = dept2

Journal Lines.Department and not = dept3

Step1 evaluates to true when tested against invoice above

Step2 evaluates to false

Step3 evaluates to false

Step4 evaluates to false (this is where I'm extremely confused).  What do i have wrong?  Is there a right way to set this up compared to what I have?