I get hired to implement software or run a project for the client. Until the recent job, I had three in a row where myself and the contract team were not invited to any event. We would have team building sessions and invite the employers staff but it would not be reciprocated.

For me it is not a big issue, for the employers it creates a great deal of ill will with thier own employees. Had one job with a MAJOR (top five in cash on hand in the U.S.) where I took over a job that was staffed by all internal resources. Went live and was not invited to the go live lunch, so they saved twenty dollars. Two employees complained at the table with the CIO that I wasn't there and came back with an attitude. Took them aside and told them to stay calm, and schedule a lunch with just the small group of devlopers and business analysts. Billed the company two extra hours, paid for a nice luncheon, problem solved. The company lost money on the transaction and the core team got two lunches.