Click the Office Button and choose Word Options. Select the Advanced category and, in the Editing options section, select the Keep track of formatting checkbox. Select the Mark formatting inconsistencies checkbox. Click OK.
Another way to see this difference is to notice that, relative to the stars, the Sun appears to move around Earth once per year. Therefore, there is one fewer solar day per year than there are sidereal days.
Sidereal year, from one time a particular star is in a given position to the next time 365.25636 days. Anomalistic year, from the time the Earth is at its closest to the Sun to the next time 365.25964 days.