After upgrading to my new Xeon 2680v4 system I am experiencing this issue:
Adding Samsung NX1 HEVC UHD files in small batches at a time fills considerable amounts of RAM, whose usage will go up for a couple seconds and then subside again. This way I can make a project that contains an hour or more of HEVC footage.
In the end Vegas uses only about 2.5 gigabytes of RAM when everything has loaded.
Once I save and reopen that project while building the preview frames, Vegas quickly uses all my 16GB of RAM and the computer becomes unusable, Vegas slows down to a halt, Audio becomes choppy until I finally lose Video out and have to restart the PC.
So something in building those previews is hogging the RAM for too long. This does not happen with H.264 files.
Assigning only 8 Threads to Vegas did not help.
The issue is present in Version 14 build 178 as well as 211.