Last line of paragraph always lower (line spacing is higher)

I often had this problem with InDesign CS3 (and I think CS2 also).
When composing a paragraph in InDesign, the last line will often be further away,
is that a known issue about InDesign. I checked the paragraph option (space afters, space befores, etc) and there is nothing: All line in the paragraph have the same characteristics.
There are no characters in subscript or superscript mode.

What could cause that?

Thank you

Louis

G5, Leopard, Suitcase X1, Creative Suite CS3.