SUMMARY
FileChooser mangles filters if mimetypes and globs are mixed. Even ignoring current_filter in some cases. 

I'll be using gdbus and GVariant format out of convenience. I initially encountered this behaviour in a GTK program after porting FileChooserDialog to FileChooserNative. GTK dialog worked as expected.


SCENARIO 1
Two filters both using globs.

$ gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.FileChooser.OpenFile "" "Please choose a file" "{ 'filters': <[ ( 'Windows Executable/MSI Installer', [ (@u 0, '*.[mM][sS][iI]'), (@u 0, '*.[eE][xX][eE]') ]), ( 'Any file', [ (@u 0, '*') ]) ]> }"

{
    'filters': <[
        (
            'Windows Executable/MSI Installer',
            [
                (@u 0, '*.[mM][sS][iI]'),
                (@u 0, '*.[eE][xX][eE]')
            ]
        ),
        (
            'Any file',
            [
                (@u 0, '*')
            ]
        )
    ]>
}

RESULT
Works as expected with "Windows Executable/MSI Installer" as the default filter.


SCENARIO 2
Filter with one mimetype and a filter with one glob

$ gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.FileChooser.OpenFile "" "Please choose a file" "{ 'filters': <[ ( 'Windows Executable', [ (@u 1, 'application/x-ms-dos-executable') ]), ( 'Any file', [ (@u 0, '*') ]) ]> }"

{
    'filters': <[
        (
            'Windows Executable',
            [
                (@u 1, 'application/x-ms-dos-executable')
            ]
        ),
        (
            'Any file',
            [
                (@u 0, '*')
            ]
        )
    ]>
}

RESULT
An additional filter "Windows Executable, Any file" is shown and selected. It only shows files of type application/x-ms-dos-executable.


SCENARIO 3
Filter with two mimetypes and a filter with one glob

$ gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.FileChooser.OpenFile "" "Please choose a file" "{ 'multiple': <false>, 'filters': <[ ( 'Windows Executable/MSI Installer', [ (@u 1, 'application/x-ms-dos-executable'), (@u 1, 'application/x-msi') ]), ( 'Any file', [ (@u 0, '*') ]) ]> }"

{
    'multiple': <false>,
    'filters': <[
        (
            'Windows Executable/MSI Installer',
            [
                (@u 1, 'application/x-ms-dos-executable'),
                (@u 1, 'application/x-msi')
            ]
        ),
        (
            'Any file',
            [
                (@u 0, '*')
            ]
        )
    ]>
}

RESULT
An additional filter "Windows Executable/MSI Installer, Any file" is shown and selected. It shows nothing.


SCENARIO 4
Two filters both using globs, but with the second filter as the current_filter.

$ gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.FileChooser.OpenFile "" "Please choose a file" "{ 'filters': <[ ( 'Windows Executable/MSI Installer', [ (@u 0, '*.[mM][sS][iI]'), (@u 0, '*.[eE][xX][eE]') ]), ( 'Any file', [ (@u 0, '*') ]) ]>, 'current_filter': <( 'Any file', [ (@u 0, '*') ])> }"

{
    'filters': <[
        (
            'Windows Executable/MSI Installer',
            [
                (@u 0, '*.[mM][sS][iI]'),
                (@u 0, '*.[eE][xX][eE]')
            ]
        ),
        (
            'Any file',
            [
                (@u 0, '*')
            ]
        )
    ]>,
    'current_filter': <(
        'Any file',
        [
            (@u 0, '*')
        ]
    )>
}

RESULT
Works as expected with "Any file" as the default filter.


SCENARIO 5
Filter with two mimetypes and a filter with one glob, but with the second filter as the current_filter.

$ gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.FileChooser.OpenFile "" "Please choose a file" "{ 'filters': <[ ( 'Windows Executable/MSI Installer', [ (@u 1, 'application/x-ms-dos-executable'), (@u 1, 'application/x-msi') ]), ( 'Any file', [ (@u 0, '*') ]) ]>, 'current_filter': <( 'Any file', [ (@u 0, '*') ])> }"

{
    'filters': <[
        (
            'Windows Executable/MSI Installer',
            [
                (@u 1, 'application/x-ms-dos-executable'),
                (@u 1, 'application/x-msi')
            ]
        ),
        (
            'Any file',
            [
                (@u 0, '*')
            ]
        )
    ]>,
    'current_filter': <(
        'Any file',
        [
            (@u 0, '*')
        ]
    )>
}

RESULT
Works as expected with "Any file" as the default filter and no extra mangled filter.


SCENARIO 6
Filter with two mimetypes and a filter with one glob, but with the first filter as the current_filter.

$ gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.FileChooser.OpenFile "" "Please choose a file" "{ 'filters': <[ ( 'Windows Executable/MSI Installer', [ (@u 1, 'application/x-ms-dos-executable'), (@u 1, 'application/x-msi') ]), ( 'Any file', [ (@u 0, '*') ]) ]>, 'current_filter': <( 'Windows Executable/MSI Installer', [ (@u 1, 'application/x-ms-dos-executable'), (@u 1, 'application/x-msi') ])> }"

{
    'filters': <[
        (
            'Windows Executable/MSI Installer',
            [
                (@u 1, 'application/x-ms-dos-executable'),
                (@u 1, 'application/x-msi')
            ]
        ),
        (
            'Any file',
            [
                (@u 0, '*')
            ]
        )
    ]>,
    'current_filter': <(
        'Windows Executable/MSI Installer',
            [
                (@u 1, 'application/x-ms-dos-executable'),
                (@u 1, 'application/x-msi')
            ]

    )>
}

RESULT
An additional filter "Windows Executable/MSI Installer, Any file" is shown and selected. It shows nothing


SOFTWARE/OS VERSIONS
Operating System: Gentoo Linux 2.17
KDE Plasma Version: 6.2.4
KDE Frameworks Version: 6.8.0
Qt Version: 6.8.1
Kernel Version: 6.12.4-xanmod1-dist (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 3600 6-Core Processor
Memory: 47.0 GiB of RAM
Graphics Processor: AMD Radeon RX 5700 XT