problems with a field within a block (ACAD2006)

Hi,
In Autocad 2006, I created a block called door_symbol.
door_symbol is comprised of the following:
- a block called door_leaf (comprising some geometry drawn at an
overall size of 1 unit) - two attributes - one field, which references door_leaf's z-scale
When I insert this block into a drawing, everything works hunky dory, however sometimes, when saving, regenerating, or resizing/scaling an instance of the block, all the geometry and attributes disappear, leaving me with just the field - now reading 0 or 1 - and some far flung defpoint thingamies. If I try to insert another instance of the block, the geometry of all the preceeding blocks returns but the field now reads '#'. Is this a bug, or have I done something wrong?
TIA
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