pausing slides -

Captivate 4! That is a long time ago, but I think it is the same reason as for later versions: if you execute a simple action with an interactive object (click box is one) to do something, like showing a text caption, at the same time the playhead will be released. Not sure, don't have 4 anymore. In versions since 5 this can be solved by replacing the simple by a standard advanced action. And I remember vaguely the terrible UI for advanced actions, you could try, you need only one statement.

Why choose Standard over Simple action? - Captivate blog