Due to the way EZproxy operates, it may be possible for cookies created by other web applications at your institution to pass through EZproxy to database vendors. This behavior can impact databases being proxied, and specifically does impact IEEE Xplore.
To correct this problem, you need to run at least EZproxy 1.4g, along with a database configuration like this:
Title IEEE Xplore
Your exact Title and URL lines may vary from the above. The key pieces are the appearance of Option DomainCookieOnly before the Title and Option Cookie before the next database definitions Title line.