Taxonomy, Terms and Weights

I have set up a Taxonomy with various Terms.

Each Term has a Relations/Weight which seems to affect the order in which they show up in the Build/Taxonomy/ListTerms as well as the order in which they are displayed in a Taxonomy Widget created for them.

I say 'seems' because these Relations/Weights and Widget orders change arbitrarily when the save button is hit in the Build/Taxonomy/ListTerms page.

Also the order of the Terms can be adjusted by drag and drop in the Build/Taxonomy/ListTerms page, but it is not clear if this affects the Relations/Weights or the Widget ordering or if the ability to drag and drop is unrelated to any of this (although dragging and dropping would be a -lot- easier than editing and adjusting the Relations/Weights.)

Are there some rules that I can follow for this to make more sense?

Thanks!