Bug # 1
Here is what I see as bug behavior:
- When setting gear wheel Settings > View > Auto image size > to Fit image to window ,and unchecking 'Reset Auto Image size settings with next/preview file',

the program does not use that setting in the preview tab when the program is re-opened (I'm in Browser view). Each time I open XnViewMP it resets toolbar menu View > Preview > Auto Image Size > to 'Fit image to window, large only'. When I go back and check the gear wheel Settings > View > Auto image size > it correctly still shows 'Fit image to window' - but it doesn't seem to be holding and using that setting on program restarts. Each time I restart (I'm in Browser view) I have to go to toolbar menu > View > Preview > Auto Image Size > and manually select 'Fit image to window'. Then it only holds and works for that program instance. If I restart XnViewMP I have to reset it again. Shouldn't it be holding that setting in the ini file for program restarts, especially if it's designated in the main Settings menu? I opened the xnview.ini file at
C:\Users\<username>\AppData\Roaming\XnViewMP\xnview.ini with Notepad++ and searched for ''Auto image ', 'Auto image size', 'Fit image' & 'Fit image to window' and it finds nothing.
In Settings > Fullscreen > Auto image size > I have it also set to 'Fit image to window' and that setting works correctly, and the program is holding that setting.

When I open an image in Fullscreen it always opens correctly as fitting the image to window size. So that Fullscreen 'Fit image to window' setting is held from program restart to restart.
Bug # 2
In Settings > Interface > Keyboard > SPACE > it's set to 'Next File'

This works when in Fullscreen only. But when in Browser view, if select a thumbnail item, pressing the spacebar does nothing. It does not advance to next file. in Browser view Left and Right buttons do correctly advance to next thumbnail item, just not spacebar.
For reference ... when I installed the program, after install it opened the 'Startup Wizard'. I left the ini file location at default 'User(System)' . I left the 'Other Settings' at defaults. The only thing I changed was to check the 'Add Browse with XnViewMP to context menu'

And it correctly added the Browse with XnViewMP to context menu.