Slides already viewed in a presentation

Hi Folks!

I'm searching for a solution to an issue with resume presentation not always working for my students and was wondering if you might be able to shed some light on a few questions I have . . .

Let me start by providing an example of the suspend_data file for a student who worked through a portion of a presentation.  Upon re-entering the presentation he answered 'Yes' to the prompt asking if he'd like to resume where he left off, but was forced to start over from slide 1.  The suspend_data information below was taken AFTER he was forced to start over again.

viewed=1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30

|lastviewedslide=1|1#1##,15,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,

1,1,1,1,1,1,1,1,1#0,0,0##1

One thing I've noticed is that the suspend_data file in these situations is that it looks the same as it would if the student had answered 'No' to the resume presentation prompt. Am I right?

1.  Is there anything that could cause a 'Yes' answer to the resume presentation prompt to act as if 'No' had been clicked instead?   Maybe something in the student's operating environment?  Or something within the LMS? 

2.  I was always under the impression that the ability to view slides already viewed within a 'locked' presentation was based on the viewed slides showing in the suspend_data file.  However, that seems not to be the case.  I tested it and after answering 'No' to the resume presentation prompt, the suspend_data file will still show all the slides previously viewed (viewed=), but it does not allow the user to freely move around and view slides already viewed.   So my question is how does a presentation decide which slides have already been viewed, thus allowing the user to jump around to other viewed slides within the presentation? 

Thanks for any help any of you can provide in answering these questions.