Saying they are prone to shorting and catching fire is probably too strong. Yes it can happen but I would not say it is likely or they are prone to it.
As far as travel rules, for travel in the States I believe the batteries in the VML fall under the "larger lithium battery" restrictions and are limited as one larger lithium ion battery installed in a device, plus up to 2 spare larger lithium ion batteries in carry-on luggage. You are not supposed to have any loose lithium batteries in your checked luggage (only installed in a device).
You can find more info here:
http://www.tsa.gov/travelers/airtravel/ ... eries.shtm