I was running a sub salac Garchomp and its hp hit 17% (from poison) and the salac berry didn't activate. I don't know if this is because of the server, but I have never experienced this on the official server.
Berries activate before poison so if poison damage takes you lower than 25% your berry will activate next turn. That's how it works on the official server too.
If I recall correctly, Salac Berry can only be activated by an in-turn effect. End of turn effects (poison) don't trigger it.
Just to be absolutely clear, this is a Shoddy bug. The Salac Berry should definitely activate right after the poison damage lowers your HP to 25%. I just tested it in-game to double-check. Pinch Berries always activate the moment the holder's HP is reduced to 25% or less.
I couldn't tell you whether the main server has this bug fixed or not, but I'm guessing not.
EDIT: On a side note, those who are asking about where to report bugs, I wouldn't bother. I don't think I've ever seen a bug disappear from the Shoddy site's Bug Tracker. This is not to say that bugs are
never fixed, but we're coming up on the one-year anniversary for the discovery of some well-known bugs and they've never been addressed. Generally the bugs that are fixed are the ones pointed out by high-profile players and those that are very easy to fix. You're better off fixing it yourself if you know Java. If you don't know Java, find somebody who does or just live with it.
Also, don't hold your breath for Double Battles on Shoddy. I've seen the code and Shoddy Battle looks like it was written with only Single Battles in mind. It'd be almost easier to code a whole new simulator than to try to adapt the existing code.