Inconsistent behaviour using relative URLs in HTML block.

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I have a page on my site, say localhost/concrete5/page1.

I have added a html block onto the page page1 with one link to itself:
<a href="./">Page 1</a>.

However, "./" actually brings me to "localhost/concrete5/" - which is what I would expect "../" to do.

So, I tried to get around this by making the link "./index.php/page1" - and it works! Until I reload the page a couple of times (I have the cache turned off) - and then suddenly it links to "localhost/concrete5/index.php/page1/index.php/page1"!

Does anybody have any idea what is going on here?