PES5 problem with sidebacks/wingbacks

[NX24]

When I'm in possession, one of my SBs/WBs occasionally wanders to the center of the pitch (right in front of the backline) instead of hugging the sidelines. I spent hours meddling with these settings:

- positioning of SBs/WBs
- different players
- number of CBs
- offensive arrows
- defensive arrows
- backline A/B/C
- sweeper / line defense / normal
- man marking / zonal marking / covering

Nothing has any effect! This isn't normal, is it? I got all my players to act exactly as I want them to, except for those bloody wingbacks.