I have the following item:

Soldier's Story
2H Rare Polearm
192.4 dps
174 - 231 damage
0.95 aps
20 - 47 Cold Damage
179 to Life after Each Kill
Level Requirement Reduced by 6
1 Open Socket
Required Level 42

This weapon is not included in the results for a search for 2H weapons up to lvl 42, but is included in the results for a search of 2H weapons up to lvl 48 (lvl 48 being the lvl that would be required to use the weapon if the -lvl requirement mod was not factored in). I have posted this item to the AH once before, just re-posted again and figured this out.

I believe this is happening for all items with the -lvl requirement modifier, as I have an armor with the same mod that was also not being included in search results for its modified required level. I haven't reposted the armor, given the above issue.