There is a bug in storagemanager which would allow it to create files with the wrong length in the filename. There is an assertion in the Sync class that checks the length.
cpimport causes the initial problem when it creates the rollback files. The assertion happens if/when the sync class starts synchronizing those files before cpimport can finish and do the rollback.
This is related to
MCOL-3459, but is the minimal fix needed to fix this specific problem for 1.4.4.