Not getting a quick answer, I took the long time for a second install.
Both installations run fine and completely independently.
The second one (unpatched) flies quite a bit easier than the patched version and easier than real life models it seems to me.
The patched version 1.9 (including heli patch) flies much more difficult and in fact seems harder to fly than real models.
Nice to have both versions instantly available for using either one as the mood strikes.
Maybe I'll have 3 installed on the same computer after I get the addon hangar pack!

EDIT: Observations based on flying helicopters only, no planes.