Hi everyone.
I just want to let you know, that with the latest Opera version (116.0.5366.127) I don't experience this behaviour anymore.
@leocg no, it was just a text with a dot. Like in my example above, where it simply was "file_name.pdf" Literarily this text in my original post in this thread.
@burnout426 It was Opera One, unfortunately, I wasn't able to find a time to test properly with different build, on a clean environment etc. The only thing I know is that it was happening on both of my laptops. And it was happening on every page, every time. No exceptions. Any plain text with this pattern: string.string
So I assume it was some sort of combination of a specific Opera release and something specific to both of my Windows environments.
Plus it looks like @Unknow0059 experienced it too. So it wasn't just me and my environment.
Anyway, everything's OK now. I'm happy, the life is good. 