Yes, the deemed contributions would actually be fairly rare. There are a certain number of circumstances that avoid unpaid debt being a deemed contribution. Notably, a financial institution can write off the debt as being unpayable, and in that case it wouldn't be a deemed contribution.
If that wasn't the case and it is a deemed contribution, in theory it would be potentially an offence, and a determination would have to made whether it was a wilful contravention of the contribution limits or not.