I downloaded the latest Beta Portable and the same problem remains.
It's easier for me now that I can enter the url that Browser Chooser is opening.
This works: C:\Users\username\Documents\Projects\projectname\index.htm
This doesn't work: C:\Users\username\Documents\Projects\project name\index.htm. Browser choose attempts to open this address instead: name\index.htm
Hope that helps!
Thanks for looking into this bug :)