Just found a problem during attempt to build a project that is deep within branches.
During cleartool get -to filename element_path command cleartool failed with "cleartool: Error: Operation "get cleartext" failed: Filename too long." error.
It appears as TeamCity uses cleartool get command instead of just updating a view and then using files it got from the ClearCase. Generally speaking it is a good idea. However it doesn't always work and that's especially true if you use branches and try to build a deeply branched version of the project.
Guess it would be a bug report.