One work around - use the trade function in the bottom LEFT, the problem seems to be linked to the trade dialogue. I can trade and save ONLY if I use the bottom left trade icon.
ALSO - I just was able to use the dialogue trade after I used the what I mentioned above and save...so interesting...
This did not work for me. My save capability still breaks after interacting with a vendor.
I am thinking it is likely my "Party Limit Be Gone" mod but I have not gone through my mod list one at a time to troubleshoot. Unless the problem persists I will just wait for an update.