Import v. Insert

[Paul A. Rubin]

There's a thread on the user list from someone running LyX 2.3.4.2 on 
Ubuntu 18.04.4. The File > Import File > LaTeX (plain) file dialog fails 
to show .tex files with the default (LaTeX) file filter, but does show 
them with the "all files" filter. In contrast, Insert > File > Child 
document ... dialog with the default filter (LaTeX/LyX documents) does 
seem to work for him.

Can anyone point to a difference in how the file filters are set up that 
might provide a clue. FWIW, I am unable to reproduce the problem on Mint 
(which is Ubuntu-based), but my file dialogs look substantially 
different from his (and not just because er spricht Deutsch). Could this 
be a Qt setting issue?

TIA,
Paul