With DBD::Sybase multiple active $sth require multiple physical network connections.

There is a way to have multiple simultaneous queries active on a single connection by using client side cursors, but this seriously limits the type of queries that can be sent so I didn't implement it.

That said - you can have multiple $sth open at the same time as long as only one is active at a time (meaning that it has been executed and that not all results have been fetched yet.)

Michael