The problem was caused by cases when some problem has relative paths in it's final location.
For example, Valgrind DRD tool can produce urls like this:
/build/glibc-t3gR2i/glibc-2.23/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S
If we try to open such problems then assertion inside IndexedString constructor happens (serialization/indexedstring.cpp:256):
Q_ASSERT(url == url.adjusted(QUrl::NormalizePathSegments));