When InDesign pushes short words to the next line
By default InDesign uses a muti-line composer (called Adobe Paragraph Composer) which tries to be helpful by looking at your paragraphs and balancing out the quantity of words per line. The result is usually good but sometimes you can end up with large spaces at the end of seemingly random lines. If this is a not working for you a easy fix it to select the misbehaving paragraph and choose the Adobe Single-line Composer option in the justification section of your paragraph style.