Since upgrading from v5.1 to v5.2 of Sibelius I've found that the VSL Ensemble Special Edition soundset (ie the 5.2 version provided by VSL or a 'doctored' 5.1 version of the original) does not work correctly, at least on my PC.
e.g. it does not default to sustain, slurs do not invoke sustain/legato making it useless.
I reverted to 5.1 and it was fine including with VSL's new 5.1 soundset. Upgrading to v5.2 (and no other changes e.g. to the Dictionary) recreated the problems above.
Anyone wanting to upgrade to 5.2 might want to make sure they've still got the Sibelius 5.1 installation file before doing this.