Here's my theory, combined with the bevel, the low-mass, high-drag design of the booster causes the rocket to partially "drag separate" after the initial thrust period of the motor ends. Then when the ejection charge goes off, the now vented recovery bay simply allows the pressure to blow past it, and the rocket turns over at apogee, and comes in without the parachute deploying.
A possible fix would be to add tape to the shoulder to tighten up the joint. However, depending on local conditions (heat, humidity, the tape's properties, etc.) this may become too tight (preventing deployment) or too loose (still allowing drag separation). Thus many people opt to mod the nosecone by eliminating the bevel in some manner.
Personally, I plan on cutting away the bottom of my BD's nosecone, and adding in a plywood bulkhead (and possibly a payload/av bay), while still closing the area that the bevel was located. While this will increase the area that the parachute, shock cord, and wadding can be located, it will also decrease the area that the ejection charge has to pressurize (by sealing off the unused volume of the nosecone) and thus increasing the pressure of the ejection charge.
Another possible mod would be to glue (or tape in) some foam (like Styrofoam, or the stuff used for dried floral arrangements*), then shape it to fill the bevel.
*I'd recommend testing any foam for its flammability before doing this.