I think most part time people are treated differently, but prolly not intentionally. You aren't there 5 days a week. They are. Some people might resent that, some might not care.

It sounds to me like a blend of two things. You are hyper sensitive that you might have inadvertantly missed a deadline, and that the office doesn't care for you. One prolly casts a shadow on the other.

Maybe on Monday, or one day last week when you were not in the office, the boss announced he was leaving on Monday afternoon for the week. Maybe he didn't realize that you didn't know? Maybe he realized on Monday, when you weren't there, that he needed that project done ASAP, and he finished it? It could have been simply bad timing.

As to how people treat you- if you are saying a cheery 'hello' each time you come in, and maybe dropping a compliment or two every once in a while, and getting the cold shoulder- that's one thing. I would say that isn't very nice of them. What can you do? Not much, IMO. Say 'hello' and do your job. I have found it difficult to work in environments where there is tension in the air- I hate that.

Any chance that any of them know you are looking for full time work?