The WebKit2GTK 2.14 (and 2.14.1) version of the library (as used in Yakkety) has introduced a bug which causes the "notify::title" signal to be called multiple times then it is necessary, posing a problem for applications that use the document's title as a bridge between JavaScript and Python.
This issue is not present under 2.12 (as used in Xenial). This bug affects WebKit2 powered applications such Ubuntu MATE Welcome and Polychromatic. Downgrading 2.14 to 2.12 in Yakkety results in expected behaviour.
Attached to this bug report is a Python example that reproduces this bug, which needs extracting to /tmp as it reads a basic HTML document.
Under 2.12, clicking the "One", "Two", "Three" links prints "One clicked", "Two clicked", etc in the terminal once, which is the expected behaviour.
Under 2.14, clicking the links prints "One clicked", but then a subsequent click on "Two" and "Three" results in "xxx clicked", a null, then "xxx clicked" again, which indicates a bug when the notify::title signal is triggered.
Status changed to 'Confirmed' because the bug affects multiple users.