The main feature of Pokemon GO is using GPS data from your device to walk around the game world in real time and track down wild Pokemon or make your way to gyms and PokeStops. It has been pointed out by some users in the past that Pokemon GO's GPS tracking can be spotty, and may even credit players with far less travel than they actually partook in, on some occasions. Thus far, the origins of the issues were unknown, and the issues seemed to only happen in-game. A Redditor by the name of cameocoder, however, documented a glitch that points to Pokemon GO quite possible messing with a device's GPS, even while it's running in the background and other apps are being used.
To put the glitch to the test, cameocoder fired up the GPS-based activity tracking app Map My Run. One walk was taken without Pokemon GO sitting in the phone's memory and running in the background, while the other was taken with the game in the background. Despite the game being in the background, the Map My Run app mapped out the sort of erratic, straightened-out, and somewhat shorter distance route that Pokemon GO has been accused of capturing for players. Since Pokemon GO was in the background, it is probable that the limitations that the game places on the use of the device's GPS are on a hardware level, and persist as long as the app is running in the back of the house
cameocoder used a Nexus 5 for the test, and has noted that they have been thus far unable to produce a similar effect on a different device. While this means that a good portion of Pokemon GO players may be able to breathe a sigh of relief, it also means that the reason for the GPS anomaly inside the other app could not be determined. While this could have been a one-off incident or triggered by some setting in cameocoder's device, Pokemon GO players who use other apps that take advantage of their device's GPS may find it a good idea to close up the game once they're done catching Pokemon.