sqlite error database is locked when using sqlite3 command line

I use sqlite3 command line, from bash.

I spawn multiple processes, all trying to insert into the same sqlite database file.

I often get "database is locked".

According to my reading of documentation (http://ift.tt/1EgOAsk) , this should never happen: "SQLITE_LOCKED means the source of contention is internal and comes from the same database connection that received the SQLITE_LOCKED error".

sqlite3 command line is single-threaded, so I would expect SQLITE_BUSY in this situation, but not SQLITE_LOCKED.

Code:

doit() {
   sqlite3 /tmp/db "insert into foo(a,b,c) values(1,2,3);
}

doit &; doit &; doit &

I tried adding PRAGMA busy_timeout=2000; and PRAGMA locking_mode=EXCLUSIVE; for the heck of it, but it didn't help.

sqlite3 -version
3.8.9 2015-04-08 12:16:33 8a8ffc862e96f57aa698f93de10dee28e69f6e09