After a few more tests, the problem is also present with:
-IE 8 (Windows XP 32 bits)
-IE 10 (Windows 7 64 bits)
-Firefox 22 (Windows 7 64 bits)
As I suspected, the problem is relative to the new portal for Lazarus (which is quite great , BTW). If the forum is reached directly, this does not occur.
Way to reproduce the problem:
1/ Open your browser
2/ Clear all your history data (cache, cookies, ...). This is absolutely mandatory for this test.
3/ Go then directly to the Lazarus home page:
http://www.lazarus.freepascal.org/ . This is also mandatory. (Remark: you must read the forum as a guest, without being logged).
4/ Click on the forum link. As seen in the attached capture (see capture2.png), you should now have a "PHPSESSID" data add for the forum link (but not for the other URLs).
5/ Choose a topic in the forum: using the last posts part (i.e. at the right of the web page), or just by browsing and selecting any topic inside the forum.
6/ Try to find a topic with an internal link (i.e. a link to another topic or another post in this forum) inside a post. For instance this topic (I'm adding such a link at the end of this post, for test purposes). Click on it. Another window or another tab should open. It should be the targeted post or topic; but instead, it's the home page of the forum, because the URL is invalid.
Additional remarks:
-as indicated before, if you reach the forum directly, this does not occur:
.
http://www.lazarus.freepascal.org/ , then forum, ===> Possible problem
.
http://forum.lazarus.freepascal.org/index.php ===> No problem
.
http://forum.lazarus.freepascal.org/index.php?action=forum ===> No problem
-when logged in the forum, the PHPSESSID data (it's a cookie, as far as I can see) seem to be cleared, and so the problem is no more present.
-when browsing the forum topics (possible problem case), the links are OK because the PHPSESSID data are added at the very end of the URL. Sample (OK):
http://forum.lazarus.freepascal.org/index.php/topic,21660.0.html?PHPSESSID=c566eb142895ea270a97dfab8af8ed63
-but when an internal link inside a post is used, the PHPSESSID data are
inserted into the URL, and that's why the obtained URL is invalid. Sample (wrong URL):
http://forum.lazarus.freepascal.org/index.php?PHPSESSID=c566eb142895ea270a97dfab8af8ed63&/topic,20511.0.html
While it should be:
http://forum.lazarus.freepascal.org/index.php/topic,20511.0.html
or eventually
http://forum.lazarus.freepascal.org/index.php/topic,20511.0.html?PHPSESSID=c566eb142895ea270a97dfab8af8ed63
Test URL (see "Way to reproduce the problem", step 6):
http://forum.lazarus.freepascal.org/index.php/topic,21660.0.html