I forget which programming talk I watched which pointed this out, but one extremely common example of this in Java is recreating subsets of the Collections API. I've done this before, heck even the Java standard library is guilty of this problem. When a class has a full set of get/put/has/remove methods, it is often not actually hiding the complexity of its component data structures.
Good example of a bad abstraction. If you're speaking the language (or "abstraction") of sets, you should see certain terminology: union, intersection, disjunction. These words are not part of the Java Set interface.
I would actually argue that the Collections API itself is a pretty good abstraction. It is often the case that conceptually I just want to work with multiple things and properties like order, duplicates, random access, etc. are not particularly important (in fact, requiring them adds inherent complexity). It's very useful that a vast amount of the standard library data structures conform to this interface or can create data views that conform to it.
