truncated yum -- why?

[Benjamin Sher]

Dear friends:

[Using Scientific Linux, which is based on RHEL 4]

When I type the command:

yum list installed

I get a read out that starts from A to Z.

But when I type the command (as user or root):

yum list available

I get a list that starts with the letter p (pearl...) and ends in z.

What would cause this to happen and how can I correct this? I recall 
that it didn't happen this way at first.

Benjamin