Explicit typing breaks type inference

[Bart Bogaerts]

Compare

http://dtai.cs.kuleuven.be/krr/idp-ide/?src=596cf4f635777444b75614fd79862c16

with

http://dtai.cs.kuleuven.be/krr/idp-ide/?src=88eae07e9dcc11e6d8ee023c161ac1c2

In the explicitly typed one (the first) type derivation fails (on some internal variable), despite correctly printing the right type for that variable. The second one (untyped) works for some strange reason.