The patch from https://bugreports.qt-project.org/secure/attachment/30642/0001-Fixed-dead-keys-on-Windows-QTBUG-8764-QTBUG-10032.patch introduces issues with Cyrillic layouts that support dead keys. An example would be the layout from http://ilyabirman.net/projects/typography-layout/ which is often used by translators, editors, correctors and the likes.

To reproduce:
1. Install a layout with Cyrillic and dead keys support
2. Open a Qt application that uses Qt version 4.8.5.0 or later
3. Switch to Cyrillic input (Russian in the case of aforementioned layout) and type relatively fast

This results in garbled input as illustrated in the attached screenshot (of Blizzard's Battle.net client). Same results can be produced in Psi+ (an XMPP client) messaging windows.