Ask PG/HN: Plings in titles ...

I've had a vague impression for a time that something like this has been happening, but now I've seen it for definite and for real. I submitted an item - http://news.ycombinator.com/item?id=2127187 - putting plings in the title, and yet when I checked the submission, the plings had gone.

Then I edited the title, and the plings turned up.

Can someone cast any light on the processes here? Are the permitted characters in titles different in initial submissions as opposed to edits? If so, is this deliberate?

Thanks. I await answers with interest.