findById returns no results even with correct ObjectId

Problem

Configuration: Mongoose 4.0.5, MongoDb 3.0.4, Node 0.12.4 Issue does not appear on Mongoose 3.8.30 My database has the following data: [code block] I query it with Mongoose using the following syntax: [code block] which returns null for both error and user. Strangely enough Mongoose's debugging shows the following, correct query: [code block] which queried directly on MongoDB finds the expected data: [code block] I tried various alternatives such as directly initializing an ObjectId object or taking an ObjectId from a `find()` result which leads to no results either. As stated above reverting back to Mongoose 3.8 resolves the issue.