Thanks Guys.. I have been reading CU5 for SQL 2012 and it says :

A database transaction log continues to grow after you upgrade to

SQL Server 2008 SP2 or SQL Server 2008 SP3

Yes I know it says 2008 and I am 2012 and I have not upgraded.

Microsoft page.....

http://support.Microsoft.com/kb/2777772

Looks like this may be reoccurring bug they have had for a while 2005 , 2008 and still in 2012!

I have applied sp1 as it includes CU5 and all is still stable. Fingers crossed it says that way!