bv,
It looks like you’re using DIGITS when redirecting to showprop.php and lowercase LETTERS when redirecting extensionless filenames to the actual PHP files. IF that’s the case, make your character range definitions match ONLY the correct set of characters, i.e., [0-9]+ for digits and [a-z]+ for lowercase letters. That’s the simple version of an answer that would solve all the problems presented.
Also, I like MZ’s comment about using the Last flag.
Once again, though, if you would like to learn more about mod_rewrite, I created a rather lengthy tutorial years ago (as a Mentor … before my Team Leader days) and, although it was abbreviated by SitePoint, I still have the long version (with examples) online at http://datakoncepts.com/seo.
Regards,
DK