Other than Quark (and almost *every* other DTP software), InDesign does not typeset "per line". Instead, it balances hyphenation and white space distribution over an entire paragraph. The result is far better and consistent spacing.
... those horrible days (and nights) of tweaking line after line, paragraph after paragraph to make it look better in my QuarkXPress layouts.
You can "avoid" the very best possible spacing by disabling the Paragraph Composer, and switching back to the dumb Single Line Composer.
It's one of the major differences between Quark and ID.
ID has a "paragraph composer" as will as a single line composer like Quark's, and it's on by default. When you use the paragraph composer the text is constantly analyzed and spacing adjusted for the best fit and appearance (according to the spacing algorithm and your justification settings) for the entire paragraph. If you force a line break, ID may adjust all the lines above as well as the lines that follow.
If this is a "serious problem" you shoud probably witch to the single line composer. You'll find a drop down for it in the paragraph style definitin dialog under the Justification settings, or you can change an individual paragraph as a local override from the Control panel flyout menu.
Most of us whove been ID users for some time find the paragraph composer to be one of the strenghts of ID, and feel it generates nicer looking text than a single line composer.
Thank you. It seems to be a very simple explanation and solution. I do need the ability in certain instances to bump lines without having the whole paragraph reflow so I think I'll just select those specific lines and use the single line setting.
Thanks for your help!