Here's a previous thread that answers your question. http://www.reddit.com/r/AskHistorians/comments/1k51y5/was_there_ever_a_war_in_which_a_informal_truce/cblis4d
Here's another thread that talks about similar events. http://www.reddit.com/r/AskHistorians/comments/25uskn/was_there_nonhostile_interaction_between_allied/