error/2 problem with undefined error numbers

error(4, a) is ok:

[eclipse 15]: error(4,a).
instantiation fault in a

undefined event is ok:

[eclipse 16]: error(a,a).
WARNING: no handler for event in a

but an undefined error number (e.g. 3) gives:

[eclipse 17]: error(3,a).

no (more) solution.
no error handler: [eclipse 18]: 

This occurs with both the development and normal ECLiPSe.