The GFCI breaker compares the current from the hot wire (usually the black wire) with that returning to the panel via the neutral wire (usually the white wire). Occasionally when someone later adds an outlet or other wiring device to a circuit, they will tap into the neutral of a separate circuit downstream from the point of GFCI protection. This effectively completes the circuit and gives you power. The main risk in wiring this way is overloading the neutral wire. With a regular breaker you wouldn't notice a problem (unless you overloaded the wire to the point of burning it out) because it does not compare hot and neutral current. With the GFCI protection at the outlet itself (not at the breaker), you won't notice the problem if the neutral tap is upstream of the GFCI, but you will notice it if the neutral tap is downstream (after) the GFCI. The reason is because now when there is activity on the other circuit (remember, both circuits are sharing this neutral somewhere), it creates an unexpected difference in current along the neutral. The best fix is to find the shared neutral and correct that issue. When that is not possible, avoid using a GFCI breaker, and use a GFCI outlet instead. You may have to use multiple GFCI outlets, each protecting only itself, wired so as not to protect anything downstream in the circuit. If you don't know where the shared neutral is and it happens to be downstream of one of your GFCI outlets, then you'll still get tripping at that outlet if it is wired to protect downstream. As far as safety goes, even with a shared neutral you're probably alright (officially, it's a potential hazard) if it's just on convenience outlets that don't have large loads, but as you've found the GFCI tripping can get annoying. It could also be a problem with how the GFCI breaker is installed in your panel. The load (black) originates at the breaker. The neutral for this circuit must be connecte to the neutral screw on the breaker, not the panel. The pigtail on the breaker goes to the neutral bus in the panel. If any other neutral comes between the neutral for the circuit and the neutral screw on the breaker, you'll likely have tripping problems. Good luck.