Travel Time Calculation Issue

There seems to be an issue with calculating the number of months it will take for a ship to travel to a distant location.  In the first screen snapshot below, you can see a Probe that has 17 moves.  In the second screen snapshot, you can see the destination that I have selected for the probe and it shows that it should take a little over 9 months to get there.  In the third screen snapshot, I have right-clicked on the 9 month marker and you can see that it now shows that it should only take less than 7 months to get there.  This does not happen every time, but it happens often enough to be annoying and worth taking a look at.