SIGSEGV in QWebEngineScriptCollection

I tried to implement some user scripts support, looking at Otto browser sources.
And faced with SIGSEGV inside QWebEngineScriptCollection::clear() and QWebEngineScriptCollection::insert() methods. I tried to call these methods from QWebEnginePage::acceptNavigationRequest() reimplemented method, and also just from QWebEnginePage::loadFinished() signal handler.

This issue happens only on pixiv in manga viewing mode (pixiv registration may be needed for accessing these URLs: http://www.pixiv.net/member_illust.php?mode=manga&illust_id=<some_number>), but works ok on other pixiv pages and other resources. Unfortunately, i unable to build webengine with debug symbols.

Segfaulting both on x86 and amd64 arch with 5.7.0-1 WebEngine package from Archlinux repo.