I can't find the ukpsf link at the moment, and my copy is down, so Bad Moji to the rescue
Cylinders have two burst disks which are effectivly fuses.
A high pressure one which is positioned at the back of the regulator and holds the cylinders full pressure and to protect you from anything happening to the cylinder due to overfilling.
A low pressure one which is positioned at the front of the regulator, this protects your gun from the regulator failing and excessive pressure getting through
If one fails then you should investigate why, because it may not just be due to overfilling but could be a problem with the regulator, dirty air, or perhaps just the burst disk getting old after repeated fills
Always verge on the side of caution, be aware and have happy paintball