As most of you know, propane cylinders are not designed to be completely full! Overfilling beyond the designed capacity can result in leakage (at best), or in extreme cases, cylinder failure (usually a previously damaged cylinder) from overpressurization or from flame impingement should a leak ignite. The one pound cylinders are made for single use so I would suspect they might be more prone to failure and problems (cheaply made) than the cylinders designed for repeated use. Over the years (of use of one pound cylinders), I have had several leak for various reasons (none from being very old). By the way, I did not refill them. Now, I avoid them totally and use a 10 lb. cylinder stored on my swim grid to operate my BBQ. Lasts for about 2 months of relatively heavy use, and I feel is much safer and avoids the garbage associated with the 1 lb disposables. Safe storage is a concern when it comes to the 1 lb bottles. Ensure they are stored in a well ventilated area where any leakage can make it's way quickly overboard (remembering that propane is heavier than air) and also away from ANY potential ignition sources.
A little storey. On one boat we looked at when boat shopping (happened to be an American Tug 34), when I looked into the cockpit lazerette (a totally enclosed space) I found that the current owner stored a plastic gas can (about 10 liters) and a 20 lb propane bottle down there. Also in the space (laz) was an electric stern thruster motor, 2 lead acid batteries, and a dedicated battery charger. What a recipe for disaster!!!! Open ignition sources in the same enclosed space as he chose to improperly store flammables (gases from the liquid fuels). Darwin at work, IMHO.
There is enough energy stored in a 1 lb propane bottle to potentially do very serious damage to any boat (including destroying most smaller boats), so ensure you store them properly (safely), replace them often (routinely) and at the first sign of any damage or deterioration of condition, and treat them with respect for their potential.
FYI, I strongly advise against freezing the bottle to try to "squeeze in" more propane than was designed should you decide to refill them, especially in hot climates where the contents are more prone to increases in pressure caused by the heat or sun exposure!
There is a reason why propane tanks (refillable) must be tested and certified, personnel doing the refilling must be properly trained (certified), and the cylinders are NOT filled beyond their listed (stamped on the bottle) capacity. Propane is quite safe if used and stored properly, but it can have severe results if not!
I am not being overly dramatic here, I have seen first hand the results of the careless use of propane and it isn't pretty.