Funnily enough, I have a similar problem in my new MX5200 HST with 4 in 1 bucket. The tractor has only done 50 hrs (just completed the first service - whoa, expensive filters but OEM is a must). Shortly after I bought the machine, the clam or jaws of the bucket started doing some strange things, like not releasing pressure when the control button had been released, to the point the hydraulic pump was labouring and all other controls (boom lift, bucket crowd) were non functional. It's taken the dealer a while, but he came to our property the other day and was a bit miffed. Believes it's a stuck valve in the control module. Warranty, thankfully. The tractor must be trucked back to the dealer (350 kms round trip) this week and the module replaced (a A$1700 or $1000 US part apparently).
When this first started, it was only occasional, however more recently it's been happening more frequently and now if I turn the clam operating switch on, the clam does its own thing and opens/ closes for a while... quite dangerous really.