I have never experienced it. I setup an oval every year under the tree and I've never had an issue. However, with a layout that is permanent, and has more than one loco and perhaps accessories, it would be best to make sure there are no "loops" It makes sense theoretically. For my larger setup downstairs I have a loop and make sure there is no feedback by just insulating in one spot. That can be insulating rail joiners or cutting a gap. For gaps, they say they should be filled with something to prevent them from closing up, but I've never had a problem. Of course, now that I've said it, I expect I will. LOL
I just read this on the DCC++EX website in the subsection named "Details to Make Engineer's Propellers Spin" in the section about "What's New in DCC++EX?"
"Next, the Waveform Generator needed 2 timers and interrupts, one for the Main track signal and one for the Programming track. The Uno only has 3 timers. So 2 of them were already tied up for sending the DCC signal. Since the programming track sits idle most of the time, and both signals were always being generated to the input of the motor board, processing power was being wasted that could be put to use for something else. In addition, because of the way the Arduino is designed, we were forced to use jumpers to connect pins on the Arduino to those on the motor board. Our new design eliminates the need for jumpers!"
After watching that video and thinking about it a bit further I began to realize that a simple one train small loop probably would not present much of an issue.
But the method you mention as just insulating in one spot using either insulating joiners or cutting a gap (then filling that gap with a nonconductive material) actually makes the best sense.
Going to finally hook up a separate short programming track and a 30" piece of flex track as my main line to do some initial testing in just a few minutes. A friend loaned me a couple of locomotives to wet my appetite, and to get my own complete train set instead of just experimenting with getting the the Arduino DCC controller up and running and really using it.
That's the spirit! Once you start, you can't stop.