Confusing cut along line result . My misunderstanding,wrong model or bug please help.

I have start to model rectangular water storage tank but when I use the result along line of cut section the result make me confuse.

I search from the forum about the concept of result along line and found it at :  

http://communities.bentley.com/cfs-file/__key/telligent-evolution-components-attachments/13-275895-00-00-00-27-05-91/Results-Along-Line-_2D00_-explanation-of-terms.pdf

I have model another one to check. The result of test model same as describe in above document.

But when compare to my water storage tank model. Location of cut at the cover slab and result has different 

Please kindly comment . I'm new in STAAD Pro.

Best regard 

Siwalak Khamnurak