Okay, there's some bad stuff about crossings lately - mesh cars are going nuts after some sim crossings. Our investigation showed that there's nothing wrong with our scripts(basically we're using only one function that applies any force to the vehicle - llApplyImpulse with TRUE flag for local axis, so there's no chance it can give us such crap).
I made a JIRA issue ticket with our problem(https://jira.secondlife.com/browse/BUG-4084), so LL probably will fix it some day. Till that time please cross sims with SUPER CARE.
Sorry for inconvenience.