In the original game, you would lose the extra defence points awarded by armor, whenever you gained an experience level. This is a patch that should fix that bug. I also stopped you from gaining experience when your level is already at maximum.
KingMike's Translation
http://www.emuxhaven.net/~kingmike/index.html
Zombie Hunter
Bug Fix Patch v1.0
Release date: 1/31/2006
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Original Title: Zombie Hunter
Bug-fix release to the original game.
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This patch is to fix what I see as a bug in the game.
Whenever you gain an experience level, the level up routine
writes the base defence value for the next experience level
over both the "armored" and base values of the current level.
This is a patch that changes the routine to calculate
your current armor's rating along with the "base" value.
I also modified the Experience routine, so it should ignore extra
experience awarded if your Level is already at maximum.
Hopefully, this'll take out those pointless level-up messages that
don't mean anything at maximum level (I just hacked the RAM in
FCEUltraXD as a test. When I set my level to 31, I didn't get
any experience. So, it should work if you actually play to get
level 31 experience.
This patch was made on the original Japanese ROM, but it should
work on the translation, as I don't think I changed the bank where
the levelup data is stored.
Zombie Hunter (Japan).nes - NOINTRO
CRC32: CC5A32D5
MD5: ADC42539A052110AF3DBA31B94330574
SHA-1: 087BCE6F9D3BE307B973CE050681CEFA9D97449D
SHA-256: 91DFB1A0C29F78C5D5B0A582C737C62103C4009AD5E2C20FDECD0C22A8648A48