Makesdna fails to detect issues in 32 bit code that can only be resolved by adding a padding pointer. We never noticed since we ourselves no longer build for 32 bit, but debian's 32 bit builds got bitten by this A rather extensive explanation on why this is alignment requirement is there can be found in this comment: https://developer.blender.org/D9389#233034 Differential Revision: https://developer.blender.org/D12188 Reviewed by: sergey, campbellbarton