Reproduction:

1. Create a new Writer document.
2. Type in some text, say "text r more text"
3. Select the single 'r' character (note: we have text on the same line both before and after the 'r')
4. On the menus, choose Tools | AutoText
5. Type in "dummy autotext" in the Name field
6. Type in "da" in the shortcut field
7. Click the AutoText menubutton, and choose New (Text Only)
8. Replace the word "more in your document with "da" (so there is still text both before and after the shortcut)
9. Press F3

Expected result: "da" is replaced with "r", so that the document text is now:

  text r r text

Actual result: "da" is replaced with "r" _and a paragraph break_, so the document text is now:

  text r r
  text

If I edit the autotext, the document opened for editing has the paragraph break; but deleting it and saving does not help.