Incorrect MMFF94 atom type assigned to the second N atom in molecule CNC(=O)N(C)N=O. See the relevant test in ForceFieldConfiguratorTest class.
Another molecule that exhibited the same failure is CCCC(C)(C)COC(N)=O. The N mmff94 atom type is N instead of NC=O. The corresponding N atom hoseCode is N-3;C(=OO/,C/).
The bug has been solved and a patch has been made for that. The problem was the not complete form of the mmff94 atom type pattern. Patch will be added tomorrow. See that and the relevant unit test.
Applied to master now.
Daniel, this patch too does not seem to have been applied to master yet. Bugs should not be closed until the fixes hit the main CDK repository.