tt.round not working properly with d>370

ttones=tt.ones(10,400)
tt_test=ttones*0.
for i in range(50):
    tt_test=tt_test+ttones
    tt_test=tt_test.round(1e-3)
    print(tt_test.r[10])

It seems like tt.round is not really controlling the rank growth for the above example (d=400). If one uses, say, ttones=tt.ones(10,200) instead, the loop finishes instantly with a rank-1 final TT array. 
