Your assumption that the plugin thinks the version of the player is not the right one seems to be correct.
In the admin section, the player version is listed as "unknown".
To investigate this issue further, I installed a new wordpress site with a new jwplayer plugin in the folder v1_3_2.
Surprise ! The player version is listed as "current player : JW Player 5.4.1530".
A quick check showed that a post with a progressive video download now works in the folder as expected as HTML5 with the Safari and Chrome browsers.
I was quite sure to have done serious tests in the past and I looked what were the differences between this new installation and
the preceding installations. The main difference was that I used now a laptop with Vista running with Flash enabled browsers, wheras the
other installations have been done on a laptop running Windows 7 with Flash disabled browsers.
I went back to the Windows7 laptop and was able to reproduce the same failing test results as described at the beginning. To validate the results, I used also a Desktop PC running Windows7 with Flash enabled browsers. Same negative result.
My findings today are :
If WordPress is installed in a folder one level up to the root directory on an hosted server using a PC running Windows7, the installation of the JW Player Plugin 1.3.2. fails, because
the player version is listed as unknown, even if the player is reinstalled.
I compared all the files in the different folders on the server without detecting a anormaly.
I think the problem is related to the path management in WordPress. I will continue my investigations. In the mean time, I know the workaround : Vista.