I don't think that Tie::File expects the file to be changed while it is tied to an array. Tie::File builds an index of the lines in the file, and if the file is changed, the index won't be updated until the tie is broken and renewed.

If you need need interprocess communication, consider one of the alternatives (for example discussed in perldoc perlipc, or File::Tail, or creating new files for each item of information.