Use this c++ test:

main()

{

  int         _xx;

  _xx = _xx + 2;

  return _xx;

}

"query-replace" loses the edit region.

Works in Emacs 23.3. Broke in GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)

of 2019-08-29

1. Select region from line 2 '{' to line 8 '}'

2. Do "query-replace" to begin "Query replace in region"

3. Do Double-click left mouse to select '_xx' on line 3

   -or-

   <down-mouse-one> "mouse-drag-region" to select '_xx' on line 3

4. In "Query replace in region:" window do <mouse-2> "mouse-yank-at-click"

   to insert '_xx'.

5. Via keyboard hit "Enter" key, now you see:

   "Query replace in region _xx with:"

6. Via keyboard type '_yy' and 'enter'

"Query replace in region _xx with: _yy"

7. Nothing happens because the region in step (1) has been lost.

    It should ask to replace 4 ‘_xx’s in the region.