I noticed two strange things about the the listing of the tribes in Numbers 13:4-15. Firstly, the order of the tribes is as follows:
Reuben, Simon, Judah, Issachar, Ephraim, Benjamin, Zebulun, Manasseh, Dan, Asher, Naphtali, Gad
This order does not seem to follow any other tribal order that we have seen elsewhere in the Bible. Commentaries have suggested various possibilities, such as that they were ordered by age, ordered by stature or that the tribes approached Moses in a disorderly fashion, and he appointed them one by one as they approached him. However, none are particularly compelling.
Additionally, Josheph is mentioned with the tribe of Manasseh, rather than with the tribe of Ephraim, who appears first, and with whom Joseph is usually associated. (There are some nice suggestions to explain this discrepancy as well, see Hizkuni and others.)
I was also struck by the strangeness of the name of Issachar's representative, Igal, the son of Joseph. Some other interesting points relate to the similarity of names between Zebulun and Manasseh's representatives.
This all made me wonder - is it possible that there was an early scribal error or other corruption in which lines were copied out of order or modified somehow, and that the "Joseph" appearing in the tribe of Issachar was originally part of mentioning the tribe of Joseph prior to Ephraim? Does anyone discuss this? I personally was unable to come up with any single (or even double) modification that could resolve this satisfactorily, but I would like to hear what others think.