The original purpose of this functionality was to join two horizontal alignments + children (vertical + cant) together. The assumption was that the two alignments can be joined, which means that the ending xy coordinates and tangential direction of the first alignment matched the starting xy coordinates and tangential direction of the second alignment. If this condition was not met then the software will not join the alignments.
You can send me your .alg and I will look at it! Maybe I made the software to restrictive!
R. W. Bradshaw