I'd say the criteria could be,
- will this be useful for other visitors?
- is there a better place to ask this? e.g. should you rather ask this in the issue queue? or should you rather figure this out yourself?
- have you done your own research?
In this case, the bug has already been reported in the drupal.org issue queue. So yes, technically there is "a better place to ask this".
But, these core bugs usually take quite a long time to be fixed, since any fix in D7 needs to be completely backwards compatible. Plus, walking through the tons of comments on a drupal.org issue can be quite a waste of time.
We can expect that a number of people will simply look for a workaround, and don't want to wait for core to be fixed. This is where drupal.stackexchange can fit in.
This being said, there are a few things I would expect or hope from the person asking the question on drupal.stackexchange:
- Do at least as much research that you can post a link to the respective issue on drupal.org.
- Explain why you turned to stackexchange, instead of just participating in that issue.