Applescript: Why does this happen?

• I have this down to this snippet in a drop files application. This is the entire application:

• And I have what seemed like random behavior down to a single example:

When I drag this selection:

the app displays the dialog. Once. It runs once.

But when I drag this selection:

It displays the dialog twice. For some reason grouping an html file with the folders causes it to run once, but trade the html for an rtf file, and it runs twice. But no matter how many items are selected, it never runs more than twice. But why more than once?

Sometimes the first dialog displays a single path and the rest the second time up. But sometimes it displays all the paths at once, but twice. I must have some fundamental misunderstanding of the On Open function.

Why is the app running twice (sometimes)?

Many thanks in advance for any help with this!