I think we're talking about two different things.
The issue with content blocks is, as fadum points out, that someone may just play around with different templates for fun, some templates containing just the {content} tag and others containing also {content block='name'} tag(s).
Then it would be very sad to lose content that has been added to a content block when that person too late is realizing that that template didn't include a content block tag...
My suggestion is that content entered into content blocks should always be kept in the database and only deleted if the entire page is deleted.
What WiseQ is writing about in his bug report has nothing to do with content blocks, but only the fact that a page that previously had the content-type content still has a template assigned when it is made into a section-header. But of course a section-header cannot use a template, so the template associated with a content item should be deleted when that content item is made to a section header.
Also, the content is kept for that page when it becomes a section header. But that is a very different thing to selecting a different template for a page, as section-header and content are two completely different types of content. I think that a page that is changed from the content-type content to the content-type section header should have its content deleted, like WiseQ writes in his bug report. But to make sure, there should then be a warning saying that content will be deleted when clicking save.
So to me, we talk about two different things and personally I agree with both iNSiPiD and WiseQ
