Using MadCat's ButtonBomb, I got a client disconnect every time I've tried so far, except for a local server + client + InSim. Considering the amount of data being sent (over 54KB of button text alone) I'm not really surprised.
Client & InSim: Windows 7 64bit
Windows Vista 32bit (LAN) - lost connection
Wine on Ubuntu 10.04 (LAN) - lost connection
Windows 7 64bit (local) - connection OK
Nov 01 12:02:35 InSim - TCP : ButtonBomb
Nov 01 12:02:40 FATAL TCP ERROR : BUFFER SIZE
Nov 01 12:02:40 Leave @ 11212 : Degats
Nov 01 12:02:40 Lost connection to Degats^L (Degats)
Interestingly, when testing with localhost, the buttons didn't get displayed on screen if the client was already on the server when the InSim connected. When the client joined with InSim already running, the buttons displayed fine, but the text in the chat history went missing - probably to do with the many overlaid buttons.
On the LAN servers, the buttons caused a disconnect whichever connected first.
I'll try do some more tests later with my own test app, hopefully with some more OS & network combinations as well as different numbers of buttons etc.
BTW MadCatX, the "Packet count" option in the ButtonBomb is never used in your code, so it sends out 238 buttons every time.