I'm not a user of OO3 but the earlier versions e.g. 2.4 don't have this problem. I just checked.

However it is possible that I'm changing the spacing in a different way to you. The way I do it is to press F11 to bring up the style list, then right click on the style for paragraphs (First line Indent) and select modify, then go to spacing and change it to Double.

If you do this and also verify that the spacing for the headers is single then you should not have a problem int he future. These changes do seem to be remembered in the RTFing in oo 2.4 at least