MT CSFB abnormal LU

[nhake]

Hi all
I am confusing about the Location Update when MT perform CSFB. Could you please help me to make clear?
I set up the CSFB call as bellow
- MO, MT : 4G preferred mode
- Call duration: 10s
- Time interval: 15s
The phenomenon at MT as I describe below
- After the 1^st call MT do TAU as normal: TAU accept with TAC 34705/LAC 62207
- 2^nd call at MT: UE fall back to 3G and reading the SIB1: LAC 62207
- MT request RRC connection for answering incoming call
- MT perform RAU as normal: Old RAI: LAC 32770/RAC 24 and Additional Old RAI: LAC 62207/RAC: 20
- MT do LU at LAC 62207
- RU accept at RAI: LAC 62207/RAC 20 and LU accept at LAC 62207
- Call proceed as normal
I am wondering why MT perform LU is this case ( same LAC, not periodic updating)?
Please correct me if I am wrong?

[plannerguy]

Hi

Hope Combined LU is performed also its home PLMN.

Rgds
Plannerguy