mucaco

Hi, I have the Ultimaker 2 updated with the latest firmware. Gcode is produced with Cura 15.04.4 Sometimes it happens that the printer perform retraction, not at the end when the head is moved to the new location, but in the middle of long straight line. This usually occurs in the bottom layer. Some part of the line is than missing and can cause problems on next layers. I wonder if problem is known to anyone else, and how to prevent it. Thanks.