New Moto Guzzi Door Mats Available Now
It's a known problem with the odd Breva - the dipstick winds itself off while under way. There are various fixes to stop that - search here & on the MG_750 Yahoo site - oddly, it doesn't appear to happen with the V7
As Malik said, a known problem. As a result of mine disappearing in to the ether I carry a pair of pipe tongs to make sure mine really is tight. I believe a guy who used to be here drilled a small hole that went through the dipstick and the protrusion it resides in and locked it with an R clip.
As a "get me home" emergency measure, you might be able to find a "temporary freeze plug" or "expansion plug" to put in the hole. I had to do that once when my Morini 500 blew it's dipstick out on a ride. Should be available at most auto parts stores.