Comma splices

Separate sentences shouldn’t be glued together with commas, this is poor style.

That opening description is two separate and independent sentences. They should therefore be written as two sentences and not simply glued together with a comma (an error widely referred to as a comma splice or run-on sentence).

• If there is a genuine reason for gluing the sentences together, for instance to show a continued line of thought, you can use other punctuation for that – dash, colon and semicolon all get used.
• It happens in particular when the component sentences are short and don’t have any commas of their own; writers think harder about the structure of more complex phrasing.

This may perhaps sound slightly contrary to one of the earlier posts about not overdoing very short sentences. That was a stylistic point, though: this is purely about correct punctuation!

Prevalence: high. Comma splices aren’t good form in Dutch either. But Dutch authors perpetrate them a lot more often in English than the natives do.
Frequency: moderate. Particularly worth watching out for in shorter sentences.
Native: yes. It’s far from uncommon in native English too. Which doesn’t make it correct.