There could be other reasons. Rule number 1 in any type of computer. Nothing is guaranteed until proven. 
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Ok, missed your updated post:
You have done (1) Which is OK. Move the active layer will be default next time you start Gimp. The toggle in Tool Options is set.
What you seem to be missing is the Tool Options dock. (2) See if you can find it on your set up. You might have some other tab open. If it is missing, you can always restore it Windows -> Dockable Dialogues -> Tool Options Top of the list which shows how important it is.
No that is not normal. No idea what you did. Turn the selection off before you wreck something.
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Ok, missed your updated post:
You have done (1) Which is OK. Move the active layer will be default next time you start Gimp. The toggle in Tool Options is set.
What you seem to be missing is the Tool Options dock. (2) See if you can find it on your set up. You might have some other tab open. If it is missing, you can always restore it Windows -> Dockable Dialogues -> Tool Options Top of the list which shows how important it is.
Quote:And tried that. Blew it's mind I think. I've now got 'crawling ants' all around my second layer drawing' (which is a traced line)
I'll figure it out I guess. This has somehow become a selection I suppose?
No that is not normal. No idea what you did. Turn the selection off before you wreck something.