Combobox item is being reset to Default value

Hi,

I have two comboboxes in my form- Journal type and Posting Layer. 

When I make a selection in the first combobox i.e. Journal type, to "Allocation" and make a selection in the second combobox i.e, Posting Layer, to other than default ("Current"), it should be remembered.

Then if I change the Journal Type to other and when I again change it to "Allocation", the item in Posting Layer combobox should not be reset to its Default value.

It should be the one which I had selected previously.

Presently it is being reset to default value.

Please suggest what I have to do for this.

Thanks in advance.