Vinegar really isn't very reliable for this sort of test. Although, it's all a lot of people have access to. Try scratching up a bit of the rock before trying the vinegar test - the increased surface area will make the reaction easier, and also it will help to produce some fresh mineral, sometimes the exterior can be weathered and less reactive.
It's also worth doing a scratch test- get a nail or a beater knife, and try scratching the rock with it. If it doesn't scratch, it's probably a silicate, and most likely safe. If it does scratch... it's not necessarily unsafe, but it's more likely that it will be a carbonate.
I'd take any apparent reaction as an indicator that carbonates are present. Especially if you are restricted to using vinegar.