Just when it seemed as if a truce might be feasible, fighting has flared up again in the battle between the WAN optimisation vendors over just who can - or can't - accelerate the latest AutoCAD format for drawing files.

The vendors - not only Riverbed Technologies and Silver Peak Systems, but also Cisco and others - have been boosting themselves and badmouthing each other ever since it became apparent some months ago that users upgrading from older versions of AutoCAD found their WAN accelerators weren't working as well as they used to.

The problem was the file format: AutoCAD's developers had added compression to its 3D model data, and in the process they were scrambling the files. The result was that each time you did a save, even if few or no changes were made, it looked like a new file - and that caused problems for anything trying to cache or de-duplicate it.

For several of the companies affected, this was a good example of what can happen when programmers implement changes without considering the entire infrastructure in which their software must operate.

To pour oil on troubled waters, AutoCAD's owner Autodesk joined up with Riverbed, which appeared to be the WAN acceleration company most heavily affected - it estimates that around 10 percent of its several thousand customers are in this sector. The pair issued a joint statement, advising users on how to adjust a key AutoCAD setting called ISP (incremental save percentage) to minimise the problem.

On top of that, Autodesk said it was determined to fix the problem completely in its next major release. It said that in future it will take account of its place in the IT ecosystem, and its need to interwork with others.