h2o.runif() always returns the same vector

I am writing the code for cross validation of my models' performance.In order to split data set randomly I use this method:

h2o.runif(train.hex) 

Unfortunately it always returns me the same vector:

0.7309678 0.2405364 0.6374174 0.5504370 0.5975453 0.3332184

I've also tried to use different seeds e.g.:

h2o.runif(train.hex, seed=-1)

h2o.runif(train.hex, seed=123)

the results are always the same. What is wrong with function? I would appreciate for any hint on it.