Since today's upgrade to 1.17, the <pages> tag from the Proofread Page extension has been partly broken. The "fromsection" and "tosection" parameters to that tag are supposed to ensure that only specfic labelled sections are transcluded from the first and last pages (respectively) in the range of pages transcluded. (These are "sections" as defined by Labelled Section Transclusion.)
For concrete examples see [5,6]; in each case the end of the previous article and the beginning of the next article are included because the whole page is being transcluded rather than only the labelled sections specified.
This definitely only started happening today. It is a show-stopper bug for Wikisource, affecting as it does probably thousands, and certainly many hundreds, of works.