Built-In Blank (Three Columns) Footer Alignment Question

First let's discuss the difference between your terminology and Microsoft's:

• The tab stop markers you see on the horizontal ruler are just "tabs", and the ones in the footer are defined as part of the Footer style (which is automatically applied by default to footers). These tab stops can be set and dragged on the ruler, and set numerically in the Tabs dialog. Yes, they are used for alignment, but that isn't part of their name.
• What Microsoft calls "alignment tabs" are entirely independent of the first type -- they don't appear on the ruler, and they can't be set there or in the Tabs dialog; there is a separate Alignment Tabs dialog, reached from the Insert Alignment Tab button on the Header & Footer Tools tab. They can be set left, center, or right, but not at arbitrary distances from the margins.

The Blank (Three Columns) footer uses alignment tabs to position the center and right sections.

The neat trick that alignment tabs can do, and that regular tab stops can't do, is to reposition text correctly when the margins, page size, or orientation changes. For example, if your document contains mostly portrait pages and a few landscape pages for charts or spreadsheets, a header or footer using alignment tabs will automatically adjust its width to match the changing text column.

If someone deletes a tab and just hits the Tab key to restore it, they'll get a plain tab that will obey the tab stops in the style. To fix it, you would delete the plain tab (not necessarily the tab stop, just the tab character) and use the Insert Alignment Tab dialog to replace the Center or Right alignment tab.