Makefile won't check if updated, and just compiles anyway

Makefile won't check if updated, and just compiles anyway

My makefile will not check if there has been any updates and just compiles
if it has more than a single source file added in. It works fine with just
a single source file.
It seems that it's any source file that's not listed as the first one will
always be recompiled and linked.
SOURCES=myclass.cpp mylock.cpp
EXECUTABLE=locktest
LIBRARIES=-pthread
CFLAGS=-Wall
CXX=g++
DIR=host/
EXE=$(EXECUTABLE)
OBJECTS=$(SOURCES:%.cpp=$(DIR)%.o)
$(EXE): $(OBJECTS)
$(CXX) -o $@ $(OBJECTS) $(LIBRARIES)
$(DIR)%.o: %.cpp $(DIR)
$(CXX) $(CFLAGS) -c $< -o $@
$(DIR):
@mkdir $(DIR)
clean:
@rm $(OBJECTS) $(EXE)
@rmdir $(DIR)
Output shows problem:
stud@pc:~/Desktop/Locktest$ make
g++ -Wall -c myclass.cpp -o host/myclass.o
g++ -Wall -c mylock.cpp -o host/mylock.o
g++ -o locktest host/myclass.o host/mylock.o -pthread
stud@pc:~/Desktop/Locktest$ make
g++ -Wall -c myclass.cpp -o host/myclass.o
g++ -o locktest host/myclass.o host/mylock.o -pthread