The daylight saving time, if switched from "no" to "yes" doesn't skip an hour, instead it adds an hour to all post-times.
- if you wrote a reply yesterday on 3 p.m.
- then switch dst on
- the reply now appears with a post-time from 4 p.m.
But that is simply no true. The real post time is still 3 p.m. and so the DST Switch should behave.