It was done on purpose, you cannot open viewer on text as text us already using viewer. It will close the text app.

Can you explain the context? :)

The widget is not only rendered in viewer but also in collectives or the folder description where it is used then to open the viewer.

I don't quite remember how the behavior was if this is triggered trough text in viewer still, but would say either the close and open or another file is expected or we can safeguard this to only happen if no file is currently open in the viewer.

I don't quite remember how the behavior was if this is triggered trough text in viewer still

It wasn't. The Vue event was missing a stop and therefore the behaviour was unstable and still opening the file as if the link was clicked.

I suggest the following, until we support multiple viewer, on top of checking if Viewer supports the mime, please also check if a file is already opened in it.
Something like !OCA.Viewer.file should work 😊

Thanks, adjusted