Hi 007,
This is a good question, I will try to explain.
For Huawei LAN switch the data forwarding is made by ASIC or NP chipset.
For the ASIC CHIP, the switch will not check the MTU, so the MPLS MTU will not be set as we can see into the displayed command. Depending on the frame lenght, the switch will extract the lenght and compare with jumbo frame configuration. If the frame length is higher than configured jumbo frame value, the switch will discard the frame.
For example S5700 EI has 1600 bytes default value for ethernet frame.
[R5_U24_S5700-GigabitEthernet0/0/1]jumboframe enable ?
INTEGER<1600-9712> The max frame length, the default is 1600 bytes
<cr>
To check if the switch discards frames, you can check the jumbo counter when display interface stats:
[R5_U24_S5700-GigabitEthernet0/0/1]dis thi int
GigabitEthernet0/0/1 current state : UP
Line protocol current state : UP
Description:
Switch Port, Link-type : trunk(configured),
PVID : 600, TPID : 8100(Hex), The Maximum Frame Length is 1600
IP Sending Frames' Format is PKTFMT_ETHNT_2, Hardware address is 9017-acb6-a810
Current system time: 2016-04-13 22:20+09:00
Port Mode: COMMON COPPER
Speed : 100, Loopback: NONE
Duplex: FULL, Negotiation: DISABLE
Mdi : AUTO, Flow-control: DISABLE
Last 300 seconds input rate 1032 bits/sec, 1 packets/sec
Last 300 seconds output rate 1712 bits/sec, 1 packets/sec
Input peak rate 71856 bits/sec, Record time: 2016-04-13 22:20
Output peak rate 99941088 bits/sec, Record time: 2016-04-13 22:20
Input: 723618 packets, 87391651 bytes
Unicast: 710706, Multicast: 1351
Broadcast: 11561, Jumbo: 0
Discard: 0, Pause: 0
Frames: 0
Back to the our display command, interface MTU refers system MTU or Layer 3 MTU, so it's the maximum IP packet length.
Effective MTU discribe the value of which is smaller between interface MTU and MPLS MTU.