The first rule you have...
RewriteRule ^/0.4/ /0.4/default.aspx
...matches any URL that begins with /0.4/. Because you don't have an "end of line" symbol on that pattern, it matches anything and regardless of what comes after '/0.4/', if anything, the URL gets rewritten.
If you want to just rewrite the short URL /0.4/ to default.aspx, then just append the $ to the pattern:
RewriteRule ^/0.4/$ /0.4/default.aspx
But I would want to make the slash optional also. Hence:
RewriteRule ^/0.4/?$ /0.4/default.aspx
The question mark in the pattern above is a quantifier, saying "zero or one of the previous thing". And the
previous thing is the slash. So that pattern matches /0.4 and /0.4/, but not /0.4/hello.
Your other two rules should work just fine. (Notice that they already have the $ as the terminating symbol in the pattern)