4.0 has problems with any figure/conformer that has an unwelded mesh, as it auto-welds it on import, this changes the vertice count, which causes some morphs to explode (usually those in PMD).

They altered it in 4.5 so that while it still welds the mesh it adapts the morphs to suit so they no longer explode.

However if that's the default unposed/unmorphed shape then it shouldn't have exploded in the first place, so that one has me stumped as to why it happened.