The VDB to Spheres changed in VDB 5.0, which corresponds to the switch from Houdini 16.5 to Houdini 17.0.  The new version seems to generate spheres that lie outside the incoming VDB.

Attached .hip file should behave differently in 16.5 and 17.5.  In 16.5 the spheres stay inside the converted VDB, in 17.5 they extend outside.