http://www.ar15.com/forums/t_3_15/695738_9mm_lower_with_last_round_bolt_hold_open.html

I went with the Colt stick mag lowers...it's not an issue with them.

=P I'm really hoping I don't have to purchase a complete different lower to have the bolt hold open. At least a lesson was learned. Read the description.

Spartan 9MM/45ACP Billet AR15 Upper Receiver w/ Last Round Bolt Hold Open (LRBHO)

Specs:
-Manufactured from a solid block of Aircraft Grade 7075-T6 Billet Aluminum
-Matches up perfectly with the Spartan 9MM Glock Lower Receivers & most forged lower receivers
-Will mate with any brand of Mil-Spec AR15 lower receiver and components
-Compatible with all standard AR-15 / AR-9 components and most aftermarket parts
-MIL-A-8625 Type III Hard Anodizing (Deep Black)
-Contains integrated Last Round Bolt Hold Open (LRBHO) technology (PATENT PENDING) that reliably holds the bolt open when magazine is empty
-LRBHO feature is designed for lowers that accept Glock style magazines
-Weight: 8.8oz
-Compatible with battery assist devices including the Magpul BAD Lever and Tactical Link EBAL

Once assembled the small “hook” end of the wire form in the upper should be pushed up by the follower of an empty Glock magazine which will engage the bolt catch on the last round fired to hold the bolt in the locked position. If it does not engage, or engages before the last round is fired you can make VERY SMALL adjustments by SLIGHTLY bending the “hook” end down to lock faster or up to lock slower. They are set and function checked during assembly with brand new Glock magazines and our standard bolt catches. Because of varying magazine specs, magazine specs changing over the life of the product, different thicknesses of the pad on the bolt catch and other variables, this adjustment may be necessary with your specific parts. If you are using Magpul PMAG Glock Magazines you will likely need to bend the LRBHO spring down to engage the follower correctly.

If you want to use the PSA 9mm upper, you will have to buy the PSA LRBHO lower. I believe you can not retro fit the lower parts to make it LRBHO on the regular 9mm lower. My regular PSA 9mm doesn't have a slot cut out for the magazine, on the bolt release latch. Hope this helps.