If you're using justified paragraph formatting,the last line before you pressed the Enter key will revert to left-aligned, which is quite normal. The 'indenting' of the text is nothing more than what you'd see if you'd been using a left-alinged paragraph.

The real issue, though, is why you're pressing the Enter key in the first place - you should only be doing that (once) when you're intentionally creating a new paragraph.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]