Clive, True...but also make sure your rear master cylinder is not to full. Brake fluid expands...and if you are right on the line of being to full, just a little bit of brake drag would heat up the fluid enough to where the .5 inch free play isn't enough.
In other words, the brake drag you had might have heated up the fluid, which expanded it's normal amount, but that added to the brake drag even more. Your .5 inch could have been enough free play if the fluid level was lower....
Again, thinking out loud here...