I guess you mistaken the regular lookup mode and reading mode, it won’t remember the last viewed dictionary in the regular lookup screen.
To configure the collapse/expand feature, please follow these steps:
Tap to options menu icon on the top-right of the main screen, Tap Dictionary Group to enter the dictionary group management screen
Tap the group that you want to tweak
Select the dictionaries in the group that you want to adjust
Thank you for providing the video feedback. It was helpful in identifying the root cause of the issue. I will be reviewing the information and determining the best course of action to improve this feature.