Yup. Have seen this sometimes when you have very short pages.
The fastest easiest fix is a workaround that sounds strange:
Insert a tall thin several row table below the text. One column is all that is necessary.
Set the table lines in the properties to the DOTTED LINES outside and inside to HIDE the table.
Set the row size to 100 high or so in the table properties.
Tap the space bar a few times in each row and press ENTER a few times too.
Publish.
This adds some nonsense characters to your web page that do not show visually and do not impact the search engines while expanding the length of your web page vertically. Forces CSB to extend the colors longer because the page is longer!