Not sure if it is already tracked elsewhere.

Let's consider the following Turtle file (note the dot segment):

<http://example.com/foo/./bar> <http://example.com/bar> 1 .

If no base IRI is set then Turtle does not normalize IRIs leading to the NTriple:

<http://example.com/foo/./bar> <http://example.com/bar> 1 .

Whowever, if a base IRI is set, then http://example.com/foo/./bar can be considered as a relative IRI reference (it matches the given grammer) and must be resolved against it using RFC 3986 relative URI transformation that removes dot segments, leading to the http://example.com/foo/bar IRI and the following NTriple:

<http://example.com/foo/bar> <http://example.com/bar> 1 .