Automatic project reread when generated files change

I have several protobuf classes in my project which are generated using a QMAKE_EXTRA_COMPILER:

protobuf_decl.name = protobuf

protobuf_decl.input = PROTOS

protobuf_decl.output = ${QMAKE_FILE_PATH}/${QMAKE_FILE_BASE}.pb.cpp

protobuf_decl.commands = shell_path($$PWD/bin/protoc.bat) .\ProtocolBuffers\ \"$$PWD/bin/protoc.exe\" --cpp_out=\"$${CPP_OUT}\" $${PROTOPATHS} \"${QMAKE_FILE_BASE}${QMAKE_FILE_EXT}\"}}
protobuf_decl.variable_out = GENERATED_SOURCES
protobuf_decl.dependency_type = TYPE_C
QMAKE_EXTRA_COMPILERS += protobuf_decl

Problem is now that whenever I delete, regenerate or manually edit one of those generated files Qt Creator automatically rereads the project.

Since this is a rather big project this freezes the UI for ~30 seconds.

This did not happen in versions prior to 4.9.0