I often have three or more terminals open, doing different tasks in each; I also often have cycles of work where I'll repeat the last three commands again (three up-arrows and a return). This breaks if one terminal's commands get inserted into another terminal's history.
"Ted, the change I suggest doesn't affect the independence of your sessions as you suggest. Each shell maintains a unique history in memory so modifying the history file has no affect on running terminals. The only time the history file is read is when you start a new terminal. I recommend you try my suggestion. Really, all I am doing is eliminating the race condition that causes the bash history file to have inconsistent data.
To some degree; it depends on the amount of multitasking. I mainly care about which commands in which order when I'm looking at recent commands from that terminal; otherwise I use C-r.