strange results when using formula

hi
I have been working on this a while and have come up with a strange result ,
enter g in search plant number and click and listbox is populated (all good)
if I enter formula

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into column n to remove the first 5 charactors to leave g456 ect
now when I enter g in search plant number and click ,listbox is populated with all data not just that line
has any one any ideas as to why ,this is starting to do my head in
what I am trying to achieve is to search by number col a
or by plant ref no column d ,I moved col d to n so I could put formula together
any help would be good
thanks colin

hi
have just tried again and if you use combobox 3 the lower box and enter G you get the desired result,but if you go to sheet and enter formula in col n when you try and enter g again it populates listbox with everything
dead weird
cheers colin