Strange things happening with the Multiplier plugin.

Single object: multiply several times. OK.
Ctrl-Z to remove and try again with different parameters: OK
Delete the multiplied group: OK

multiple objects: multiply several times. OK.
Ctrl-Z to remove and try again with different parameters: OK
Delete the generated multiple objects: OK

Now try the same with a group of objects:
Group multiply: OK. (a group with groups is generated)
Ctrl-Z: generated groups are removed from the furniture list but remain in the 3Dview.
Delete: same, generated groups are removed from the furniture list but remain in the 3Dview.
Even weirder: A generated group of groups disappears when you ungroup them! And of course it remains in the 3Dview.

You have to restart Sweet Home 3D to get a correct 3Dview again without the removed multiplied groups.

It looks like the problem is related to multiplying a group instead of a single object or not-grouped multiple objects.