Table Automatically Extends Horizontally But Not Vertically?

For what reason would a table not extend vertically on it's own when an entry is made in the next row directly beneath it? On all of my sheets I could swear the table will automatically extend vertically, but on one workbook that has 10 duplicated and then modified sheets with tables (I mention that for it might have been something from the original that was copied that is the problem), the table easily expands horizontally when a value is placed in a column next in line, but not the same for the next row!