Jian,
This is the default behavior indeed and shouldn't cause any issue beyond the extra labels installed in the LIB.
You can easily change that behavior if you desire so by applying label filtering as follow:
no mpls ldp advertise-labels
mpls ldp advertise-labels for 1 to 2
!
access-list 1 permit any
!
access-list 2 deny
access-list 2 permit any
Hope this helps,
Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México