Unknown Mode Shown in the PFD Mode Annunciator Panel

[BillM]

I flew the A350 today from LSZH to EGKK.  I set up the FMC and autopilot as I usually do, and I think I did it correctly.  The flight plan had no discontinuities and the magenta line for the route appeared and was checked and confirmed from takeoff to touchdown on the ND.  However, when I got airborne and activated the autopilot, instead of NAV appearing in the mode annunciator panel at the top of the PFD, "RWY NAV" appeared.  I have never seen that before, and the inibuilds A250 manual does not seem to mention it. Also, the route was no longer shown as a solid magenta line, but as a dashed yellow line.  I disconnected the AP and hand-flew the aircraft to intercept the route line, but even if I maneuvered the aircraft close to this line, NAV would not engage.  I followed a tip given on this forum, re-engaged the AP and engaged DIR to the next waypoint, at which point NAV appeared in the annunciator panel, the route line turned to magenta and the aircraft followed the route. However, RWY NAV remained shown in blue, as if armed (see image).

Can anyone explain this?  Thanks.

Edited 4 hours ago by BillM