Yes this is a bug that has been already reported and created in FMP10. We just need FMi to now fix it.
OK more facts on the above bug. I should have written pop up menu rather than drop down (why is it called up when it drops down?) There is just a standard manually created value list driving the menu.
If I experience a field lock as described I can click one of the displayed lines and fix the problem. I did wonder if the issue was connected with the global being in the same table as the scrolled records so I also put a global field from another unrelated table in the header with the same value list/menu (no trigger attached). This also gets locked. However here is a big clue to the root of the bug. If I changed this new global to a standard field I can type into it OK but the moment I do the list jumps back to the first record. Now that is strange. Yes typing into a unrelated field in the header causes the window to scroll back to the top without the use of any script! You may want to see this for yourself. If so I will clone the db and allow someone from FileMaker to see this one. However I don't want to make the login details public so please contact me back channel.
Thanks Mr Vodka. It's good to know I'm not going mad but bad to know it is a known but unfixed bug
Thank you for your posts. (And Thank You to "mr_vodka" for including the links)
I have forwarded your comments to the original case. This has been confirmed as a problem with our Testing department and sent on to Development.
As an alternative, you can change your script trigger to navigate to the second record at the end of the script. This would only make sense if you are working in list view, however.
It is dire that this has not been fixed yet. FileMaker should be embarassed that they shipped a Devcon activities listing solution that does not work on a desktop[ if you scroll down.