[Reg 5.5.1 - 5.6.1] lupdate freezes with some projects

lupdate execution freezes after it has visited all the files i.e. after following log print:

DEBUG 1: done visiting file C:/Qt/5.6.1/5.6/msvc2013/mkspecs/features/lex.prf

And it never reaches the summary i.e. the lines with: "Updating '../translations/test.ts'... Found 5 source text(s) (0 new and 5 already existing)"

Unfortunately we were not able to create a test project to reproduce this, but a workaround was found: In the original project there are recursive includes. Renaming a file with several ring includes fixes the problem. Thus it seems to have something to do with circular includes, but the example in QTBUG-6587 doesn't reproduce the problem.

The problem was not reproducible in Qt 5.5.1. This has been tested only on Windows 10 with MSVC 2013.