This is a little bit difficult to explain, but I'll do my best...

At the moment the way you have set your title format, effects to your title filter results.

If I have
Title Format = Title

and use
Title filter = Porco Rosso, I get result Porco Rosso, as expected from Title field.
If I use,
Title filter = Kurenai no buta, I get result Porco Rosso from the Original Title field.

but...

If I have
Title Format = Original Title

and use,
Title filter = Porco Rosso, I get zero results, because it doesn't understand to search from the Title field.
If I use,
Title filter = Kurenai no buta, I get result Kurenai no buta as expected from the Original Title field.

In my setup I like to use Title Format = Original Title, but in some cases (Asian titles for example) it is easier for me to remember localized name.

I would like if the title filter would search from Title and Original Title fields, no matter how your title format is set.