In the standard replication between Outlook and Project Server, the systems inserts the project full name in the “Categories“ field of Outlook, which helps my client sorting and viewing his data . Now we see only ALLOCATUS in the categories. I imagine you need this for your synchronisation but could you have both ? (allocatus + project ID)

Allocatus sets the category "Allocatus" by default. The advantage is that it is very simple that way to find, sort, filter and group all day events, appointments and tasks from MS Project. A very nice thing is to use the Outlook 2003's conditional formatting in order to colorize all Allocatus appointments. In addition Outlook 2007 is using categories to colorize appointments. Using just one category keeps the categories list and the colors used smart.

Allocatus does not use the category field as internal id, so we are open to change the behavior depending on the clients needs.