Consider the following scenario:
1) From the MCP, ban a user and then exclude him from current ban list or vice versa
2) Now, in the banlist table there exist two records for the same user, one with the ban_exclude field set to 0 and one set to 1.

This disables the pm link for this banned && excluded user, when it shouldn't do so.
This possibly disables the email notifications for this user. It does so in 3.0.x but I haven't tested it with 3.1