Besides order activity rules, what else controls whether a record gets written to the sales ledger?

Everything I've read says that when you set up your order activity rules, the Ledger(Y/N) column controls whether a record is written to the sales ledger. However, I seem to be seeing a situation where this isn't true.

We were looking at starting our Blanket Order process at status 500 (Enter Quote/Blanket Order). In a test system I set up the order activity rules with the first step as Last Status 500 Next Status 515 Ledger Y. Processing the orders works fine, the order goes through the activity rules as we would expect. Except, the initial order line coming in at 500/515 doesn't show up in the sales ledger. If we change the order activity rules to start at 520/540 with the Ledger flag set to Y, then we do get an entry in the sales ledger when