Since Plasma 5.16, folders (or other locations) are opened inside a new Tab in dolphin (previously it was opened as a new Window). The bouncy cursor does not stop bouncing, however, after the Tab is open.
This happens in other applications, that will open new tabs (e.g. this also happens when you for example open a text document and Kate is already open)

STEPS TO REPRODUCE
1. Open a folder in dolphin
2. Open another folder in dolphin (which will create a new Tab in the first dolphin window)

(Same goes for: 1.) Open document in Kate, 2.) Open another document with Kate (will create new Tab)


OBSERVED RESULT
Bouncing cursor will remain bouncing for a while

EXPECTED RESULT
Bouncing cursor should stop bouncing as soon as there is nothing more to wait for (i.e. the tab has been opened and the appropriate content has been displayed).


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Neon Git unstable
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
You can see the behaviour in https://cdn.kde.org/promo/20190611_Plasma5.16/dolphin_cut.mp4.gif (linked from the 5.16.0 release announcement)