This is the nature of subclips. They behave like real media so their in and out points mimic the real ends. The advantage is that you can drag the end and make it loop (which you can’t do just by trimming) but as you have seen, there are no handles to trim further. There is no way around this.
As for the flicker, you are correct this is an interlace problem. Since the device you are previewing on is interlaced, there is no way around this. Even if you told Vegas to deinterlace the output the TV would still interlace it again because this is the only way it can display it.
~jr
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