I run my speed 1-mile runs on the exact same course each morning. I generally hit ~7:00/mile but this morning, my FR220 says I clocked a mile when the time was at 6:21. I should be thrilled except I know it was also ~.1 miles short of the mile (basically on roughly where I should be stopping) AND my pace on the watch was never near 6:21 at any point. I hope it was a fluke but can't be sure.
Garmin Connect also has a couple of weird issues. One is that in the records section, there is now 3 blank lines named "1k" between the 1K and the 1M records. I can't get rid of these and they only started appearing this morning. A more minor issue that's been bugging me for a while is that I might clock say 6:59 on my watch (my 1M record will say that on the watch) but when I upload it to Garmin Connect, it'll say 7:00. Or I may do a race that gets a few (i.e. more than 1) seconds added to the time when it is uploaded. Not sure why these discrepancies happen but they bug me a tad.
Overall, I really like the watch and the software!