I've finally fixed this.  The problem was with both the rack switch and the core switch having their LACP config set as 'Active'.  Setting one end (the rack switch ports) to 'Passive' was the solution here.  Having both ends set to active was causing one end or the other (or both) to continually try to bring the port channel back up when the switch was trying to shut it down.
I have a pair of S4048 switches connected together using VLT which each have 2x uplinks to my core S6010 pair (also VLT).  The servers connected to the 4048 pair do so with a link to each switch using LACP.  The problem I'm having is that when I reload either one of the 4048 switches it spends 120 seconds rapidly flapping all of the LACP links before actually rebooting.  During this time I can also see syslog messages from my core 6010 switches saying they are throttling management traffic due to excessive control messages being received from the 4048 that I've told to reload.  The 4048s are running FTOS 9.10 (0.2) and the 6010s are running FTOS 9.10 (0.1)  A sample of the syslog messages from the 4048s are: May 30 10:58:11 %STKUNIT1-M:CP %LACP-5-PORT-UNGROUPED: PortChannel-009-Ungrouped: Interface Te 1/9 exited port-channel 9.May 30 10:58:11 %STKUNIT1-M:CP %IFMGR-5-OSTATE_DN: Changed interface state to down: Po 9May 30 10:58:11 %STKUNIT1-M:CP %LACP-5-PORT-UNGROUPED: PortChannel-100-Ungrouped: Interface Fo 1/52 exited port-channel 100.May 30 10:58:11 %STKUNIT1-M:CP %LACP-5-PORT-GROUPED: PortChannel-100-Grouped: Interface Fo 1/52 joined port-channel 100.May 30 10:58:12 %STKUNIT1-M:CP %IFMGR-5-OSTATE_DN: Changed interface state to down: Po 100May 30 10:58:12 %STKUNIT1-M:CP %IFMGR-5-OSTATE_UP: Changed interface state to up: Po 100May 30 10:58:12 %STKUNIT1-M:CP %LACP-5-PORT-GROUPED: PortChannel-100-Grouped: Interface Fo 1/52 joined port-channel 100.May 30 10:58:13 %STKUNIT1-M:CP %IFMGR-5-OSTATE_UP: Changed interface state to up: Po 100May 30 10:58:13 %STKUNIT1-M:CP %IFMGR-5-OSTATE_DN: Changed interface state to down: Po 100May 30 10:58:13 %STKUNIT1-M:CP %LACP-5-PORT-UNGROUPED: PortChannel-100-Ungrouped: Interface Fo 1/52 exited port-channel 100.May 30 10:58:15 %STKUNIT1-M:CP %IFMGR-5-OSTATE_UP: Changed interface state to up: Po 9May 30 10:58:15 %STKUNIT1-M:CP %IFMGR-5-OSTATE_DN: Changed interface state to down: Po 9May 30 10:58:15 %STKUNIT1-M:CP %IFMGR-5-OSTATE_UP: Changed interface state to up: Po 9May 30 10:58:15 %STKUNIT1-M:CP %IFMGR-5-OSTATE_DN: Changed interface state to down: Po 100May 30 10:58:15 %STKUNIT1-M:CP %LACP-5-PORT-UNGROUPED: PortChannel-100-Ungrouped: Interface Fo 1/52 exited port-channel 100.May 30 10:58:15 %STKUNIT1-M:CP %LACP-5-PORT-GROUPED: PortChannel-100-Grouped: Interface Fo 1/52 joined port-channel 100.May 30 10:58:15 %STKUNIT1-M:CP %IFMGR-5-OSTATE_UP: Changed interface state to up: Po 100May 30 10:58:16 %STKUNIT1-M:CP %IFMGR-5-OSTATE_DN: Changed interface state to down: Po 100May 30 10:58:16 %STKUNIT1-M:CP %LACP-5-PORT-UNGROUPED: PortChannel-100-Ungrouped: Interface Fo 1/52 exited port-channel 100.May 30 10:58:16 %STKUNIT1-M:CP %IFMGR-5-OSTATE_DN: Changed interface state to down: Po 9May 30 10:58:17 %STKUNIT1-M:CP %IFMGR-5-OSTATE_UP: Changed interface state to up: Po 9  The config from interface Te 1/9 is: interface TenGigabitEthernet 1/9no ip addressmtu 9216port-channel-protocol LACP port-channel 9 mode active no shutdown  ....and the config from the port channel is: interface Port-channel 9no descriptionno ip addressmtu 9216portmode hybridswitchportspanning-tree rstp edge-port bpduguard shutdown-on-violation lacp fast-switchover vlt-peer-lag port-channel 9no shutdown  I'd appreciate any insight anyone can give on this.  Thanks. 
Dell/Force10 S4048-ON LACP Port Flapping Before Reload