Modify Timecode of clip to start at zero issue

I am working with clips that have embedded timecode. But I need to alter that timecode to start at zero because the producer logged the video based on a starting timecode of 00:00:00.  I should be able to "Modify Timecode" of a clip and then in the dialog, choose to use "Alternate" timecode and "Beginning" of the file. This allows me to enter timecode 00:00:00. If I hit apply I can see the timecode in the bin switch to 00:00:00 and then quickly jump back to the original timecode. So it might go from 15:23:00 to 00:00:00 and then back to 15.23.00 in 1 sec. Same if I choose multiple clips. So if I repeat this and do the exact same steps, on the second try it works.  Now the clip or clips all start at zero. So there is a bug there.

If I close the project and reopen, all the timecodes revert back to "Original"timcode and I have to do this all over.. It takes two attempts to get it to stick. And on project re-open all timecode is back to the file's original.

Mac High Sierra PP Build 13.1.5