SUMMARY
Some of the functionality around path entry does not act as expected (using Dolphin):
- The Automatic and Short Automatic completions where pressing the Tab key moves the focus from the editable location bar, rather than completing the path. 
- When pressing Ctrl+L to make the location bar editable, the path is automatically selected and pressing the Tab key moves the focus out of editable location bar, rather than completing the path entry or allowing path entry from the current folder without overwriting the current path.


STEPS TO REPRODUCE
Completion (Automatic and Short Automatic):
1. Start typing an existing path and be presented with the with some faded completion text, e.g. using '/usr/share/plasma/plasmoids/org' will present either the first sub-directory ('org.kde.desktopcontainment' for me) for Automatic completion or the shortened common path ('org.kde.') for Short Automatic completion.
2. Press the Tab key to accept the completion.

Ctrl+L Location Editing:
1. Press Ctrl+L to start editing the current path.
2. Press the Tab key to "complete" the current path entry.


OBSERVED RESULT
Completion (Automatic and Short Automatic):
- Pressing the Tab key completes the path entry as per the completion, but moves the focus from the location bar.

Ctrl+L Location Editing:
- After pressing Ctrl+L to make the location bar editable, the full path is selected but pressing Tab moves the focus from the location bar.


EXPECTED RESULT
Completion (Automatic and Short Automatic):
- Pressing the Tab key completes the path entry as per the completion and the focus stays in the location bar. A subsequent press of the Tab key would then move the focus out of the location bar.

Ctrl+L Location Editing:
- On pressing Ctrl+L the current path is selected and pressing Tab "completes" the path and allows continued editing of the path.


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE neon 5.19
KDE Plasma Version: 5.19.3
KDE Frameworks Version: 5.72.0
Qt Version: 5.14.2


ADDITIONAL INFORMATION
It is still possible to use the End key in the above instances, but this requires more movement away from the home row when typing than using the Tab key does. My expectations for what happens here comes from a combination of familiarity with shell-style completion and previous use of Nautilus for some of the path editing behaviour (the behaviour is consistent in other GTK based file managers as well).