WinXP password presto chango

Several dial-up clients using WinXP Home and WinXP Pro versions have run into the problem of their “saved” password mysteriously changing in the “password” box. They may have an 8-character password and it will work fine for weeks, then one day they’ll dial up to their ISP and the “password” box will have too many characters.. 10..11..12 and, of course, they can’t connect. Any ideas?