Premiere Pro 25.x Immediately hides custom on-screen UI upon processing event

When a 3rd party plugin based on the AE SDK advertises custom UI in the Layer and Comp windows, Premiere Pro will hide custom UI immediately after handling a parameter value change on behalf of the plugin.

One of the more obvious goals of custom on-screen controls is to allow users to tweak parameter values through a more approachable UI. Premiere Pro makes it impossible to do so for transitions, as the custom on-screen controls are hidden immediately after a change occurs.

Steps to reproduce:

- Install FxFactory 9: https://fxfactory.com/download/

- Download and install the Block Party transition via FxFactory

- Launch Premiere and add the Block Party transition in between two clips: 1.jpg

- Select the effect name in the inspector to display its custom on-screen UI:

2.jpg

- When the on-screen controls appear, click  one of the two controls that allow you to switch grid style or shape of each block:

 3.jpg- Notice that immediately after clicking the control, Premiere Pro hides all on-screen UI for that plugin. The effect header in the inspector is no longer selected. Internally the plugin is simply changing a parameter’s value, and this seems to trigger the problem.