SUMMARY
Display issue, not functional issue.

With "Toggle Auto > Parents" selected in Captions > Tags, selecting a tag with a mouse displays a checkmark next to the tag and its parents/ancestors, but when selecting a tag with a keyboard Shortcut, it only displays a checkmark next to the selected tag, and not its parents/ancestors. Either way, all parent/ancestor tags are applied to the photograph, so this issue is just about displaying the missing checkmarks.

This creates a consistency issue, and a situation where the interface does not reflect the status of the object.

STEPS TO REPRODUCE
0. Ensure "Toggle Auto > Parents" is selected

Prepare tags and assign a hotkey to a tag example:
1. Click Tag > Tag Manager from the top menu
2. Click the "+" button and create tags, "Europe", "France", "Paris" (for example), nested
3. Assign the Shortcut "p" to the Paris tag
Result is a nested list, Europe/France/Paris

Observe intended result using mouse:
1. In Album view, select an image
2. Visit Collections > Tags on the right panel
3. Click (left-mouse button) a child tag. E.g. "Paris"
4. Notice that checkmarks appear next to "Paris", "France", and "Europe"

Observe intended result using keyboard shortcut:
1. In Album view, select an image
2. Visit Collections > Tags on the right panel
3. Press Shortcut key, "p" to select the "Paris" tag
4. Notice that checkmark appears next to "Paris", but not "France, nor "Europe"

OBSERVED RESULT
Checkmarks are visible next to parent tags when using the mouse, and not visible next to parents when using a keyboard shortcut

EXPECTED RESULT
Checkmarks are visible next to parent tags when using the mouse, as well as visible next to parents when using a keyboard shortcut

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

ADDITIONAL INFORMATION
Restarting Digikam does not show the missing checkmarks