gglresearchanddevelopment/ironlanguages-main — comment on commit 630995eca293b5b0531e821b76bab7e15c4506f6
File: Languages/Ruby/Libraries/Builtins/Marshal.cs line 457
By gglresearchanddevelopment:

The 'I' doesn't get written. Below this code there was a pre-existing _writer.BaseStream.Seek(-1, SeekOrigin.Current); which overwrites it