The decimal separator in my regional settings is a comma ",". When I store decimal variables, the driver saves them as string (which seems to be by design). But the problem is that the string contains a comma for the separator and it throws an exception when the object is deserialized. For example, the number 3.25 appears as the string "3,25" in the database and won't deserialize.

Also, I tried to add [BsonRepresentation(BsonType.Double)], but the representation in the database is still a string containing a comma. This may be another bug by itself.

Here's the stack trace of one of my unit test failing:

System.FormatException : Input string was not in a correct format.
at System.Number.StringToNumber(String str, NumberStyles options, ref NumberBuffer number, NumberFormatInfo info, Boolean parseDecimal)
at System.Number.ParseDecimal(String value, NumberStyles options, NumberFormatInfo numfmt)
at MongoDB.Bson.Serialization.Serializers.DecimalSerializer.Deserialize(BsonReader bsonReader, Type nominalType, IBsonSerializationOptions options) in C:\work\10gen\mongodb\mongo-csharp-driver\Bson\Serialization\Serializers\NetPrimitiveSerializers.cs: line 744
at MongoDB.Bson.Serialization.Serializers.BsonBaseSerializer.Deserialize(BsonReader bsonReader, Type nominalType, Type actualType, IBsonSerializationOptions options) in C:\work\10gen\mongodb\mongo-csharp-driver\Bson\Serialization\Serializers\BsonBaseSerializer.cs: line 69
at MongoDB.Bson.Serialization.BsonClassMapSerializer.DeserializeMember(BsonReader bsonReader, Object obj, BsonMemberMap memberMap) in C:\work\10gen\mongodb\mongo-csharp-driver\Bson\Serialization\BsonClassMapSerializer.cs: line 305
at MongoDB.Bson.Serialization.BsonClassMapSerializer.Deserialize(BsonReader bsonReader, Type nominalType, Type actualType, IBsonSerializationOptions options) in C:\work\10gen\mongodb\mongo-csharp-driver\Bson\Serialization\BsonClassMapSerializer.cs: line 127
at MongoDB.Bson.Serialization.BsonClassMapSerializer.Deserialize(BsonReader bsonReader, Type nominalType, IBsonSerializationOptions options) in C:\work\10gen\mongodb\mongo-csharp-driver\Bson\Serialization\BsonClassMapSerializer.cs: line 81
at MongoDB.Bson.Serialization.BsonSerializer.Deserialize(BsonReader bsonReader, Type nominalType, IBsonSerializationOptions options) in C:\work\10gen\mongodb\mongo-csharp-driver\Bson\Serialization\BsonSerializer.cs: line 217
at MongoDB.Driver.Internal.MongoReplyMessage`1.ReadFrom(BsonBuffer buffer, IBsonSerializationOptions serializationOptions) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Internal\MongoReplyMessage.cs: line 94
at MongoDB.Driver.Internal.MongoConnection.ReceiveMessage(BsonBinaryReaderSettings readerSettings, IBsonSerializationOptions serializationOptions) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Internal\MongoConnection.cs: line 337
at MongoDB.Driver.MongoCursorEnumerator`1.GetReply(MongoConnection connection, MongoRequestMessage message) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoCursorEnumerator.cs: line 263
at MongoDB.Driver.MongoCursorEnumerator`1.GetFirst() in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoCursorEnumerator.cs: line 223
at MongoDB.Driver.MongoCursorEnumerator`1.MoveNext() in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoCursorEnumerator.cs: line 126
at System.Linq.Enumerable.FirstOrDefault(IEnumerable`1 source)
at MongoDB.Driver.MongoCollection.FindOneAs(IMongoQuery query) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoCollection.cs: line 493
at MongoDB.Driver.MongoCollection.FindOneByIdAs(BsonValue id) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoCollection.cs: line 529
at MongoDB.Driver.MongoCollection`1.FindOneById(BsonValue id) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoCollection.cs: line 1462
at Domain.Storage.MongoSession.Single(ObjectId id) in MongoSession.cs: line 81
at WebApp.Test.Controllers.RatingControllerTest.Rate_RecalculatesRating() in RatingControllerTest.cs: line 131