when you have mulitple archives opened in squeeze, you get tabs. (please make them reorderable with gtk 2.10. perhaps look at terminal or xarchiver code for this.)
when you close the tabs so that only one archive is left, the tabs stay there. when only one archive is left, they should disappear and re-appear when you open a 2nd archive again.

having no tabs when you open only one archive and having them when only one is left open is inconsistent. with one archive, no tabs are needed, therefore don't show them in this case.