Reproduced in <18.1>, <2018.2.0b6 SRP master @ 1fac5b8 (June 7th)>

Funky Reproduction Steps (couldn't reduce them any further):

Create a 2x2 Matrix
Drag & Create Matrix Determinant Node from 1
Drag & Create Matrix Transpose Node from 1
Drag & Create Matrix Determinant Node from 3
Create a 3x3 Matrix
Drag & Create Matrix Determinant Node from 5
Drag & Create Matrix Transpose Node from 5
Drag & Create Matrix Determinant Node from 7
Resulting Error:
Shader error in 'hidden/preview': 'Unity_MatrixTranspose_float': cannot implicitly convert output parameter from 'float2x2' to 'float3x3'

Reproduced in master, HDMasterMerge, sg/move-repository (SRP).
Doesn't have to be 2x2 or 3x3 in the order given, just has to be different sized matrices.