Playing with CTRL+C in a cqlsh session can leave the (Thrift|Native) connection in a bad state.
To reproduce :
1) Run a long running COPY FROM command (COPY test (k, v) FROM '/tmp/test.csv')
2) Interrupt the importer with CTRL+C
Repeat step 1 and 2 until you start seeing weird things in the cql shell (see attached screenshot)
The reason is, I believe, the connection (and the cursor) is not correclty closed and reopened on interruption.
I am working to propose a fix.