Changing text while wiritng

Hello, i am beginner in FileMaker and this is my situation: I have two db's, Bugs and Documents, in Bugs DB i have description of bug and another things about bugs and i can add a link to Documentation about that bug. When i write something in the Documents::Filename field i need to change it from O:test.doc to Servertest.doc. I have written script to perform it - Set Variable [$filename, Value: Get(ScriptParameter)] Set Variable [$filename, Value: Substitute($Filename; "O:";"ServerDocuments")] and this function is called by calculation in field Documents::Filename - Filename & S4HU_EventScript( "Dokuments" ; "Documents Rename"; Filename ), but thing is - when i write in Bugs to document source "O:test.doc" then it changes to ServerDocumentstest.doc, but only in Documents db, in Bugs DB it still stays O:test.doc. And in Bugs DB that field control is to set to Documents::Filename. Logically for me it have to work but it doesn't. I hope you understand me and can help me. Thanks a lot

Matej Kminek