The XPath spec. defines the string value of an element as the concatenation (in document order) of all of its text-node descendents.
This explains the “strange results”.
“Better” results can be obtained using the expressions below:
//*[text() = 'qwerty']
The above selects every element in the document that has at least one text-node child with value ‘qwerty’.
//*[text() = 'qwerty' and not(text()[2])]
The above selects every element in the document that has only one text-node child and its value is: ‘qwerty’.