Caused by rBa180c8e2ed6ce62e6a15d28a0bb7f60bb58bc0cb

So this feature should be removed from the UI, don't you think? Letting it like that really sounds like a bug to me.

Not sure why you remove it? It should work if you generate proxies in a newer blender. Just proxies generated with old blender will not work in new one.

The UI exposes this as if you could select a custom file (even having a file selector which allows you to select a file).

Selecting this file and rebuilding proxies, ignores this completely, so as far as I can see, this option is no longer used at all.

@Campbell Barton (campbellbarton), so we need an option whether we want a suffix or not? :This proxy stuff is going out of control :S

I think this is intended so you can select a file directly, if we no longer want to support that - the option could be removed.

Ok, thinking a bit more in details. Perhaps original change was to allow custom directory to be shared, by adding a suffix to the file. Now, perhaps we can ignore any suffix if there's a custom file specified? Would that support both initial change intention and this report?

It seems to me that issue is not finished. Should not it be reopened until a solution comes up?

I'll explain my use of this feature. I used to generate proxies using ffmpeg to external videos (no Blender generated scenes), so I got a very small MP4 files coded in x264, that loads and plays really fast using as a proxy.

I used to apply a filter (in ffmpeg) to make the video sharper, so the change of resolution doesn't lost so much detail using proxies. This way I don't use the generate proxy feature at all and prefer to use a custom file proxy.

This feature could be fixed or removed from the interface. I hope for a fixing, because my projects don't open correct anymore and I'm being forced to use the generate feature (a great feature, by the way). :-(