Why does ls display a non-exist file?

I want to list all the files whose name begins with uppercase:

[root@localhost /]# ls /usr/bin/[[:upper:]]*
/usr/bin/AtoB            /usr/bin/GenIssuerAltNameExt   /usr/bin/PKCS12Export
/usr/bin/AuditVerify     /usr/bin/GenSubjectAltNameExt  /usr/bin/POST
/usr/bin/BtoA            /usr/bin/GET                   /usr/bin/PrettyPrintCert
/usr/bin/CMCEnroll       /usr/bin/HEAD                  /usr/bin/PrettyPrintCrl
/usr/bin/CMCRequest      /usr/bin/HtFileType            /usr/bin/RSA_SecurID_getpasswd
/usr/bin/CMCResponse     /usr/bin/HttpClient            /usr/bin/RunSimTest
/usr/bin/CMCRevoke       /usr/bin/IBMgtSim              /usr/bin/TokenInfo
/usr/bin/CRMFPopClient   /usr/bin/Mail                  /usr/bin/X
/usr/bin/ExtJoiner       /usr/bin/OCSPClient            /usr/bin/Xorg
/usr/bin/GenExtKeyUsage  /usr/bin/PKCS10Client

It works OK, but when applied the current folder, it seem weird:

[root@localhost /]# ls ./[[:upper:]]*
snk321cq
[root@localhost /]# ls -lt snk321cq
ls: cannot access snk321cq: No such file or directory
[root@localhost /]# ls -lt ./snk321cq
ls: cannot access ./snk321cq: No such file or directory

Why display snk321cq? Actually there is no such a file.