[REG 5.12 -> 5.13] lupdate does not update .ts with translations in cpp files on subdirs projects

Having a project of subdirs type in which a translation variable is defined:

TEMPLATE = subdirs
SUBDIRS += SubProject1 \
           SubProject2
TRANSLATIONS += translations/fa-IR.ts

lupdate does not add entries to .ts file for translations in cpp files while working normal for qml files.
This was not an issue in Qt 5.12.