Are my capers still good?
I dug around a bit, and most people seem to agree that this is normal caper behaviour, though no one has made any real assertion as to why, other than that capers have varying density, and the brine does not.

The usual tests for freshness (do they look/smell/taste okay?) are recommended. Brined capers should last ~9 months from the time the jar is opened, or 3 years in a dark pantry unopened.