Unusual new behavior upon doing above install.

I have a special pared-down version of of Csound 5.06 installed in a single 
folder, with my .csd files running (in Lettuce) completely within this 
folder. No environment variables are needed or desired. Everything works 
fine.

I install 5.09 from the installer in a different location, complete 
(unfortunately) with a set of environment variables. These variables, 
especially OPCODEDIR, prevent my 5.06 system from running. The 5.09 
environment variables take over, look for everything in the 5.09 folders, 
and tell me everything is an incompatible version. (I expect that it's 
OPCODEDIR pointing to 5.09.)

To my knowledge this never happened before. The environment variables did 
*not* "take over" my self-contained 5.06 installation.

I really need to be able to run from a single folder regardless of what 
other Csound installations may be on a given machine, or regardless of what 
the environment variables are (I'm in XP here).

My understanding is that first Csound looks for everything in the current 
directory, and only if it does not find what it needs there, looks elsewhere 
(according to environment variables). This does not seem to be happening 
with 5.09.

Please someone (Michael?) straighten me out.

Art Hunkins