Rob, my guess is that you have the Quantize to Frames tool (found under the Options menu) disabled. Having this enabled ensures that frames can be moved ONLY in complete frame steps.
In your example, the two events (what Vegas calls a clip) should be perfectly lined up with each other. If they aren’t, correct this error and try again.
“how will I be able to splice it in the proper places. Doesn’t splicing follow the same rules…….i.e. on a frame??”
If by splicing you mean cutting or splitting, then yes, it will happen on a frame IF you have Quantize to Frames enabled as it will not allow you to split/splice/cut on anything other than a frame. Disable it and you can cut anywhere you want which, as I said earlier, you do NOT want to do with video.
FYI, audio for video ideally gets cut on a frame boundary as well but there are times when you need to shift and audio event a portion of a frame.
For example, I record a lot of stage plays and have a feed from the audio board on track 1 and a shotgun for ambient on track 2. Depending on what I want it to sound like, I will shift track 2’s audio around a wee bit until I like the sound it creates.