Symptoms:
Expense raised for a project which is set to Billable only comes up as Non-Billable.

Cause:
When a user raises an Expense Sheet and he has no access to selecting either the expense is Billable or Non-Billable (i.e. the Billable Column is not selected for the users to see), the billing pattern is decided based upon the Project/Tasks selection. If the Project/Task selected is set to Billable, then the expense is also Billable, if it is set to Non-Billable, then it is set to Non-Billable. However, it may so happen that when a project is set to Billable, and an expense sheet is raised against that project, the expenses get raised as Non-Billable.

Resolution:
This will happen when the project in question is not associated to a client. When no client is associated to a project, the expense sheet defaults to Non-Billable just as it would default to Non-Billable when the Project/Tasks is set to Both.