Split Tunnel SSL VPN - netbios forward deny in Local Traffic Log - Best Practice?

We have a split-tunnel SSL VPN permitting access to the internal office network; this has been set up for some time and works without issue; users are able to access internal resources and servers as required in their normal way.

Whilst checking logs on another matter I've come across a large number of denied netbios forwards on UDP 137 & 138 from VPN clients. As far as I'm aware these are not new (I went back several weeks in the logs). This discovery raises the question as to whether I should be handling this traffic in a different / better way - should it be allowed?

The fortigate is a 60D running 5.2.3. Clients connect based on authorisation via LDAP and device MAC. All clients are Windows 7 or higher.