When you have an entry selected and then apply a sort, the selected entry is deselected. The selection is reset. This only happens when the selected entry is outside of the set after the sort.
Example in my database:
- Sort by Title (default sort order ascending)
- Scroll down a little bit and select the movie “10.000 BC”
- Sort by Index (default sort order ascending).
- 10.000 BC is still selected
- Sort by Title
- 10.000 BC is still selected
When it breaks:
7. Sort by Purchase Date (default sort order descending)
8. Now 10.000 BC is not selected anymore
Now I have to use the search bar to get 10.000 BC selected again
What I would expect:
After applying a different sort column or different sort order, always follow the selected entry.
The Desktop version does this really well. I switch between different sorting and filtering quite a lot where I would like to keep my selected entry selected.
Not a really big issue, but sometimes quite annoying when I lose my selection.
In case this is seen as a bug by you. If you fix it you get a new problem in return. Sometimes (maybe in most cases) I don’t want to follow my selection after changing the sorting. Then hitting Home (Searching the first result based on the applied sorting like you would do a search) or End would be my natural thing to do to go to the top. But this is currently also not possible.
If this is not considered as a bug then I can live with the the current working OR
Always reset my selection instead when you change the sorting. Then it is clear what it is doing, now it throws me off 
Little bit out of scope of this topic but related:
When you apply a filter. For example filter on Blu-ray format while 10.000BC is selected, the selection is also reset. It would be nice that 10.000 BC is still selected because it is a Blu-ray. Only when you select a filter the current selected movie does not apply for, reset the selected entry.