Can you post a screenshot of your script? That may help folks diagnose the issue.
Also, why are you using OnLayoutKeystroke instead of OnObjectKeystroke? I don't know that using one vs. the other would change the behavior you're experiencing, but OnObjectKeystroke might provide less "interference" if you ever want to use the same script on a layout with more enterable fields.
In answer to your question, I should have posted this as an inquiry regarding onObjectKeystroke. That was how the mechanism was originally defined. I had changed it to onLayoutKeystroke as part of my many attempts to debug. It behaves the same way in onObjectKeystroke.
However, your request that I post the script led to a solution to my problem.
Before posting the script, I thought I should look at it to see if there was any extraneous code I should remove (for example, I have standard header stuff in every script and, in this script, I have an IF / ELSE that determines which subscript to perform when the Return key is detected).
Imagine my surprise when I noticed an unneeded "Freeze Window" step in the header. I apparently copied the header from another script and brought that step along as part of the copy.
Anyhow, I removed that step and the script now functions as intended with onObjectKeystroke.
Thanks for the reply!