Try this, replace your current with this:
<FilesMatch ".+\.ph(p[345]?|t|tml)$">
SetHandler application/x-httpd-php
</FilesMatch>
Then restart apache and see if that fixes it. I don't know if it will, my guess is it won't, but give it a try just to see, it's a more precise rule anyway.
But it looks to me like something in apache is not properly handling urls with a space, I tested this on my local system just to see, and when I requested:
"mysite.com/test.php "
Apache correctly rewrites it internally to
"mysite.com/test.php"
So there's I believe almost certainly another configuration that is off. But try the above and see.
Make sure to comment your stuff first, then add this in. There's probably syntax differences from 2.2 because I'm running apache 2.4, which if I remember right had a bunch of small differences in the debian configurations that led to a lot of issues, but I don't remember what they were.
I believe you can fully exclude php from this, the issue appears to be with apache2.2 and how it's handling urls, I've had this apache install for a long time, and I know I've neither added or removed any configuration that would create that situation., so you probably want to review very carefully any other non php configuration changes you might have made since installation.
The one time I have seen php code in its unparsed form on the page it was always due to the php engine not actually being correctly configured, but that's not your case since this only occurs with a space after the .php, so your php itself is fine.
As a short term hack, but NOT a solution, you can do a rewrite rule, which is very simply this:
RewriteRule ^(.*)([[:space:]]|%20)+$ /$1 [R=301,L]
I can't test this because I don't have any apache that fails to handle spaces / %20 at the end of the urls, nor do I know how to make that happen.
The rule simply says, take all spaces at the end of the line and dump them, and redirect to the actual url. Note that there are probably better ways to do this, again, it's not a situation I've ever come across so I don't know the best practices.