Based on the examples, it looks like they're only submitting forms when (1) the form uses GET (in which case, it should be idempotent anyway), or (2) the form uses POST but is submitted automatically without user action (in which case, the site designer is already using the POST request as part of a GET request).
In theory, such form submissions should be safe. If there are cases where they aren't safe, then I think it could be argued that the site is already broken, and Googlebot is just triggering an existing problem.
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