Are you sure about this?

I tried replicating this in SSRS 2005 (unfortunately I don't have SSRS 2008 installed on my machine).

With a dataset like:

Select 'Pre Order #1' as Text

union

Select 'Pre Order' as Text

And setting it for a table, I get two rows as expected.

Well, I've seen a case where if column name or alias contains #, it is replaced with an underscore.