If you haven't had the Flea for long, ask for a replacement from Blackburn; I did and they sent me two straps free of charge!
As for the strap failing, I've been using it on 25mm bars and have cut a donut shaped piece of insulation tubing which I place between the strap and handlebars to increase the diameter. This has kept the strap in near perfect condition for over a year now.
Hope this helps!
Edit: You could try and find one of the following plastic hose clamps...
