Ok, what seemed to be a bug in the library wasn't a bug (no not a feature either ) but the result of usage of old generated code with the newer library (newer as in: after weak relations support was added.).
Older generated code doesn't specify the relation type in the constructor of a relation object in the RelationClasses. Newer code does. When there is no relation type specified, the relation type defaults to 1:n. This works ok in most situations, but can fail, because in some situations the wrong table is then selected to be joined with the join expression in progress. The selected table is then sometimes already part of the join expression and thus skipped. This will result in the absence of the table in the join expression which can make the query fail.
If you see that kind of behaviour, re-generate your code.
The library released earlier today is now again available, and is OK for usage.
Sorry for this misunderstanding/bugbuzz... I'll stop acting like Microsoft
(ps: the bug popped up in the examples, which had old DAL code. These have been updated)