I don't really know how to explain it well, but when I would hold down the text to edit (every day texts) & move my finger to move it the courser, the big window would get hung up for a few sec. only happened on one of my people I was texting
Keep an eye on it and see if it continues. Often times when discussing our experiences, we like to throw around terms like 'never happened', 'flawless experience',etc when in reality, these types of minor nuances have likely occurred to us too, if even just one time. But if something only happened randomly one time....we are not likely to even recollect it.
If you have only experienced this once or twice, it very well could be chalked up to the fact that we are using complex electronic devices that simply are not perfect. If it happens regularly, then it is another story and may warrant a trip to the Apple store or a call to Tech Support after you have tried the other remedies available to you (such as a soft reset, hard reset, restore, etc).