for others bitten by this bug, using GUI scripting works around this, a bit less elegant, though.
open "OS X:Users:vangelon:Documents:Filemaker files:Pword.fmp12" -- change path here
activateapplication "FileMaker Pro Advanced"
tellapplication "System Events"
tellprocess "FileMaker Pro Advanced"
setvalueoftext field1ofwindow "Open “DATABASE_NAME”" to "ACCOUNT_NAME" -- insert account name here, insert DATABASE_NAME ("myDB" if file opened is "myDB.fmp12")
setvalueoftext field2ofwindow "Open “DATABASE_NAME”" to "PASSWORD" -- insert password & database name here
clickbutton "OK" ofwindow "Open “DATABASE_NAME”" -- insert database name here
clickbutton "Find" oftool bar1ofwindow "DATABASE_NAME" --insert database name here, too
keystroke tab -- forward tab key, moves to first text field so user can type search term, alter or delete this line if you want to start searching another field
This reads like something that would be helpful to post to Report an Issue (See tab at top of screen) to bring to the attention of the TS people at FileMaker Inc. If you choose to do so, you can include a link to this thread to save typing.