🚀 go-pugleaf

I posted this a few days ago and got no response.  Since that time, I've downloaded version 5.0 and it works fine.  However, if anyone can EXPLAIN why version 4.0 behaved as it did, I'd still be interested to hear about it.  (Original message follows) 

When viewing a .pdf file, I usually prefer to use the up and down arrow keys and the Page Up and Page Down keys to navigate through the document. Sometimes, however, for no *apparent* reason, these keys will cease to work at all, and I have to resort to using the scroll bar or the Next Page/Previous Page buttons. Also, when the arrow keys *do* work, sometimes they allow continuous scrolling (i.e. holding the key down) and at other times I have to keep pressing the key over and over again to move up or down. Can anyone explain this? Am I simply stupid, or am I doing something wrong and not realizing it?  

Specifics: This happens while using Acrobat 4.0 via Internet Explorer 5.00 (i.e. using my Web browser to view a .pdf file on the Web); Windows NT 4.0; Compaq Presario, Pentium III 500 mHz.  

This seems like such a simple issue, but I can't find any pattern to suggest why it behaves in this way. Sometimes it works, sometimes it doesn't. Any answers or constructive criticism welcome.