enum-map | A map with C-like enum keys | Map library

Edit: This was solved by moritz. I've added a note to the code on the line that's wrong.

My application is a web server talking to a game client. The server is multithreaded, which Postgres allows. When loading client data into the database, I noticed parallel requests fail with several different errors, none of which make sense to me.

This short-ish test case dumps a nested hash into the database. When run without start, it works perfectly. When run with threads, it almost always gives one or more of the following errors:

DBDish::Pg: Error: (7) in method prepare at D:\rakudo\share\perl6\site\sources\BAD7C1548F63C7AA7BC86BEDDA0F7BD185E141AD (DBDish::Pg::Connection) line 48 in block at testcase.p6 line 62
in sub add-enum-mappings at testcase.p6 line 59 in block at testcase.p6 line 91

DBDish::Pg: Error: ERROR: prepared statement "pg_3448_16" already exists (7) in method prepare at D:\rakudo\share\perl6\site\sources\BAD7C1548F63C7AA7BC86BEDDA0F7BD185E141AD (DBDish::Pg::Connection) line 46 in block at testcase.p6 line 62
in sub add-enum-mappings at testcase.p6 line 59 in block at testcase.p6 line 91

DBDish::Pg: Error: Wrong number of arguments to method execute: got 1, expected 0 (-1) in method enter-execute at D:\rakudo\share\perl6\site\sources\65FFB78EFA3030486D1C4D339882A410E3C94AD2 (DBDish::StatementHandle) line 40 in method execute at D:\rakudo\share\perl6\site\sources\B3190B6E6B1AA764F7521B490408245094C6AA87 (DBDish::Pg::StatementHandle) line 52 in sub add-enum-mappings at testcase.p6 line 54 in block at testcase.p6 line 90

message type 0x31 arrived from server while idle message type 0x5a arrived from server while idle message type 0x74 arrived from server while idle message type 0x6e arrived from server while idle message type 0x5a arrived from server while idle

Here's the code. (If you choose to run it, remember to set the right password. It creates/manipulates a table called "enummappings", but does nothing else.) The meat is in add-enum-mappings(). Everything else is just setup. Oh, and dbh() creates a separate DB connection for each thread. This is necessary, according to the PostgreSQL docs.