The behavior for V2 you describe above is not how it works (except possibly) for the first open on 3/19/2016 *if* the file was originally encrypted with V1. If you really see this behavior, something else is going on.
As I mentioned, the only situation where the behavior should differ is your action on 1/1/2016 – the initial encryption.
Both V1 and V2, regardless of V1 registry options, should set the time stamp to the date and time of the last modification of the encrypted file.
Since an decrypt + open without any change does not require re-encrypting the file, it should be left entirely unmodified, including the last modified time stamp.
AxCrypt 2 does *not* update the last modified time stamp separately just because a file was accessed + decrypted. At least not it should not, and I cannot reproduce the behavior you describe, nor does the code to do this even exist in the software so it’s hard to see how it happens.
I should stress that there *is* one situation where AxCrypt 2 actually does update the encrypted file, even though you as a user only decrypt and open it without the intent to modify it. This is the situation described earlier, when you open a V1-encrypted file with V2. In this case, V2 will re-encrypt the file in the background in order to update it to V2.
Also, please ensure that you are checking the last *modified* time stamp, not the last *accessed* time stamp. The last *accessed* time stamp is disabled by default by Microsoft in more recent versions of Windows, since it is very wasteful and time consuming.