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Under Mono, the GetHashCode method for Guid data types returns always "0". I tested it with 3.3.0 on Windows and Mono 3.6.0 on Linux.
Attached, you find a testcase demonstrating the problem.
Created attachment 8074 [details]
GetHashCode does not always return 0 but it does sometime. It needs to encode 128 bits information in 32bits.
Ok, looks like I just found some bad Guids. I now tested the number of collisions when using Mono compared to using .NET
For 100.000 Guids Mono had 4 collisions, whereas .NET had 2 (see attached demo). So nothing which is really a problem.
Created attachment 8086 [details]
collisions counting demo