Why "all" is better then everyone ? - mpls/vpls MTU problem

Follow you can see my another mpls test network.

    |------------------------|                |------------------------|   
    |   PC1 ROSv 3.28        |                |   MT1 rb411 ROS 3.28   | 
    | eth0 MTU 1522          |                | ether MTU 1522         |
    | 10.1.1.1/24            |                | 10.1.1.2/24            |
    | lobridge               |     100TX      | lobridge               |
    | 9.9.9.1/32         eth0| ---------------| 9.9.9.2/32             |
    |                        |                |                        |
    | vpls0 ip 1.1.1.1/24    |                |    wlan 10.10.2.1/23   | 
    |  to 9.9.9.3            |                |    MTU 1522            | 
    |------------------------|                |------------------------|
                                                        \   
                                                        / WLAN 5 GHz  
                                                        \  
                                              |------------------------|  
                                              |   MT2 rb411 ROS 3.28   |   
                                              | WLAN   MTU 1522        |   
                                              | 10.10.2.2/24           | 
                                              | lobridge               | 
                                              | 9.9.9.3/32             |
                                              |                        |  
                                              |    ether\              |
                                              |          bridge0       |
                                              |    vpls0/ ip 1.1.1.2/24| 
                                              |     to                 | 
                                              |    9.9.9.1             |
                                              |------------------------|

When on PC1 start Bandwidth Test with udp 1500 bytes packages to 9.9.9.3 everything works well until in /mpls interfaces I've got:

INTERFACE MPLS-MTU

0 all 1508
after I replace "all" with ether, 1500 bytes packages stops leaving router. Maximum packeges size with reach the 1.1.1.2 is 1492 bytes. Even after I'll add all PC1's interfaces including lobridge to /mpls interfaces, packeges bigger then 1492 bytes does want to reach second end of vpls tunel.
Why ?

Another question:
How can I check is there fragmented packet during mpls/vpls label add

Take a look at what I just posted:
http://forum.mikrotik.com/t/mpls-and-non-mikrotik-ethernet-controllers-and-hcl-wiki/31737/1

This may be informative to you.