I've tested Caruso's workflow as mentioned earlier and I can confirm that I got the same result, as can be seen in the attached image (imageA).
This has been repeated on Mac OS X 10.6.8 with:
* Scribus 1.4.1 (30 April 2012 Build ID: C-C-T-F-C1.12.0-Mac/Aqua Using Ghostscript version 8.71), and
* Scribus 1.5.0.svn (12 June 2012 Build ID: C-C-T-F-PC1.9.99-Mac/Aqua-64bit
Using Ghostscript version 8.71)
However, after some experimenting, editing the text directly in the frame, I found some other related oddness.
When I removed the word "one" from the first line, the tabbed numbers returned to where you'd expect them to be (imageB).
Then I added some different text "my f" to the start of the first line and the tabbed numbers moved to the right until the "f" was typed after the space, then the tabbed numbers moved to where you'd expect (imageC).
Removing this new text and typing something different again "hello there everyone" the tabbed numbers again moved to the right, visually by the same distance as the width of the added text (imageD).
All of this suggests, to me at least, that something is a bit awry with the handling of tabs as Caruso suggests but that the problem is intermittent depending on the actual text used (maybe just in the first line).
(I can't see how this particular issue could be related to the automatic tab stops but I'd be happy to learn otherwise as it all seems strange to me, and I'm guessing other new users would be similarly confused.)