RB1100AHx2 Switch1 MTU issue

I have a RB2011AHx2 ( 6.15/3.10 ) and whenever the MTU is changed on any interface belonging to Switch1 all ports drop link.

Scenario:

-ether10 is the only port in service and is on switch1
-I change the MTU on that port, it drops and I have to wait for safe mode to recover.
-I change the MTU on any other port on switch1 and the port drops..

Connected in via ether10 and try to change l2MTU on no-link port ether8

[admin@] <SAFE> interface ethernet print    
Flags: X - disabled, R - running, S - slave 
 #    NAME                                                                        MTU MAC-ADDRESS       ARP        MASTER-PORT                                                                      SWITCH                                                                     
 0    ether1                                                                     1500 D4:CA:6D:7B:6D:15 enabled    none                                                                             switch2                                                                    
 1    ether2                                                                     1500 D4:CA:6D:7B:6D:16 enabled    none                                                                             switch2                                                                    
 2    ether3                                                                     1500 D4:CA:6D:7B:6D:17 enabled    none                                                                             switch2                                                                    
 3    ether4                                                                     1500 D4:CA:6D:7B:6D:18 enabled    none                                                                             switch2                                                                    
 4    ether5                                                                     1500 D4:CA:6D:7B:6D:19 enabled    none                                                                             switch2                                                                    
 5    ether6                                                                     1500 D4:CA:6D:7B:6D:1A enabled    none                                                                             switch1                                                                    
 6    ether7                                                                     1500 D4:CA:6D:7B:6D:1B enabled    none                                                                             switch1                                                                    
 7    ether8                                                                     1500 D4:CA:6D:7B:6D:1C enabled    none                                                                             switch1                                                                    
 8  S ether9                                                                     1500 D4:CA:6D:7B:6D:1D enabled    none                                                                             switch1                                                                    
 9 R  ether10                                                                    1500 D4:CA:6D:7B:6D:1E enabled    none                                                                             switch1                                                                    
10    ether11                                                                    1500 D4:CA:6D:7B:6D:1F enabled   
11    ether12                                                                    1500 D4:CA:6D:7B:6D:20 enabled   
12    ether13                                                                    1500 D4:CA:6D:7B:6D:21 enabled   
[admin@] <SAFE> /interface ethernet 
[admin@] /interface ethernet<SAFE> set 7 l2mtu=2100            
[admin@] /interface ethernet<SAFE> 
[admin@] /interface ethernet<SAFE> 
[admin@] /interface ethernet<SAFE> 
Connection closed by foreign host.AFE>

The Log doesn’t show anything other than

: Device updated by admin
: ether10 link down

This however does not occur when changing the MTU on Switch2 interfaces, it does not kick me out ( although it might drop all the ports on that switch too, I just have nothing connected yet to test ( this is in a remote location ))

Help? suggestions?

In other side device support 2100?

The other side supports up to 9216.