Doubt adjusting seasonally with X13

[jfca283]

Hi
I have a doubt i wish you enlighten me.
I have 30 obs. And i give the order to eviews to adjust seasonally by x13.
I select the option choose best model with limits.
However, all the models estimated show
None of the models were chosen
And then if i compare the series produced by x13 is the same as the x12 output.
I've tried with other data containing more obs and this doesn't happen.
Am i wrong in something?