I emailed the same to bugs.kde.org because it is still uncertain if it is a Slimjet or KDE/kdialog bug:
kdialog - suggested wrong filetype and wrong window layout
SUMMARY
Using latest version of Manjaro KDE and Slimjet 21.0.8.0 as web browser.
When trying to 'save a page with filename' kdialog always shows a wrong filetype (xhtml instead of html) and doesn't show the checkbox at the bottom of the window...
STEPS TO REPRODUCE
1. Use Slimjet 21.0.8.0
2. Try to save a page with a file name choosen by you
OBSERVED RESULT
Note the suggested wrong filetype and wrong layout of kdialog window
EXPECTED RESULT
-
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Manjaro KDE rolling release kernel 4.20.12
KDE Plasma Version: 5.15.1
KDE Frameworks Version: 5.55.0
Qt Version: 5.12.1
ADDITIONAL INFORMATION
Investigating if the bug is due to Slimjet...
https://imgur.com/a/iNE7agQ
https://imgur.com/a/iNE7agQ