Why does '&' in (Find &) Replace give inconsitent results?

If I have a longer kind of expression in find, and & in replace, for some expressions the results are correct, but for other expressions I just get the expression words changed by ‘&’.

I am not sure it should be like that. Why does Find & Replace behave like that?

Please describe the options selected in Find & Replace window, as @dajare’s answer suggests it may have to do with these. Thanks.

The ampersand, &, when used in “Replace” should give the text as used in “Find”, IF you have “regular expressions” checked:

I hope I have correctly understood your question.