Thanks Daydreams, however marcus is neither a Oxwall customer or employee. He is a SkaDate user that hangs out here just so you are aware of that.
Some people in this world overworry about every stinking little detail when it comes to SEO and they feel that if they dont do things exactly right with every single bit of data on their site that they wont be successful in SEO. This is not true.. SEO has rules but SEO also is very flexiable as well. Normally it is their own failing that causes poor SEO but they like to blame everyone else but themselves.
The old math still works great, content content content..
Content = Users = Traffic = Good SEO.
Dont let anyone convince you otherwise. There are tricks for this and tricks for that, some work to game the system and some dont. But the tried and true method is still the same as it has always been.
Also this is very common for any website because every website has an index regardless if it is index.php or index.html, it has to have a main index page. This page can be called both ways, either by default when you enter domain.com or when you type in the full address domain.com/index.xxx
Google does not penalize you for that because this is the way the web is structured. It is impossible to have an index.php or index.html which is the main site of the page and have different contents. Well let me rephrase that, if your index is a php file i suppose you could show different sections of the file depending how the page is accessed via domain.com or domain.com/index.php but that is not necessary to do that.
Google understands how the web is created and how files are done. Don't get worked up over this one little thing, they have that handled im sure. And for those trying to game the system, thats the reason your SEO suffers!
If you wanted to you could also force just one version via htaccess so that it always loads one way or the other.
Here are the facts:
https://support.google.com/webmasters/answer/66359?hl=en
Hope that helps you.
Dave :)