added BranchGroup only sometimes visible

When I add a new new BranchGroup to my scene (Switch), it only sometimes shows up, depending on where I try to place it. If I nudge my scene by either zooming or rotating it, I can see my object (a Sphere). It stays visible thereafter. Why are there always these inconsistent invisible areas in my scene where objects don't show up until I change the orientation of the scene? My view policy is VISIBILITY-DRAW-ALL. Is this some sort of clipping problem? Any hints would be greatly appreciated. Thanks.

[510 byte] By [bryanra] at [2007-10-3 11:49:17]