Seen with server 10.6.0 (demo.owncloud.com)
Upload two files, test .txtwith a whitespace embedded before the dot, and test.txtwithout any whitespace.

When the user clicks the rename option, the difference becomes visible:

Expected behaviour: the embedded whitespace is always visible.
This is not a problem on the windows client. The embedded whitespace is shown in Explorer:

My guess is that PR https://github.com/owncloud/core/pull/38132 effected this. It changed the possibilities for what happens when the file name is clicked in the files list of the webUI. So maybe it innernametext and extension are rendered together.
@jnweiger @phil-davis https://github.com/owncloud/core/pull/38319
Just a note:
the same was reproducible for files/folders that were starting from space -
' test.txt' and 'test.txt' had no visual distinction