I frequently have a problem when entering a row of data that one or more cells will get a spurious newline at the end of their data, and that row will become double-tall. Sometimes I can guess the offending cell, click on it, backspace out the newline, which also removes the last character of the previous row, and then TAB to the next cell. Sometimes this works, sometimes it doesn't. Lately, I've just become resigned to having sheets with inconsistent row height.
+-----+-----+-----+ | | B | | | A | | C | +-----+-----+-----+
Example: If I click in Cell B, it is B plus a newline. If I hit backspace, I go up a row and remove the B. If I type B again, and hit TAB, then maybe the cell will become single-height, or maybe the cell will remain double-height.