The version of Graphviz shipped with Taverna 2.2 (Windows and OS x) is old, version 1.4 (2004); for linux users have to install the latest (2.28) or they'll already have a fairly recent version.
The dot language was extended at some point (probably with version 2.0) to allow the side of the port that an edge is connected to be specified (by adding a compass point). Later versions of Graphviz (at least from 2.26 but probably earlier) produce odd edge routing if the compass point is not specified. See T2-1874.
Unfortunately, older (pre 2.0) versions of Graphviz cannot parse dot if the compass points are added.
Version 2.26 (?) is shipped with the Windows release of Taverna
- XP - Requires .NET 3.5 to be installed
Currently version 1.4 (?) - needs to be updated to latest.
- Snow Leopard
No Graphviz shipped - need to specify that Graphviz greater than 2.0 required in the release notes.