FMC Plan disappearing on approach

Bill GustafsonKSAT (Alamo City!)I notice that when I fly a plan in VNAV and LNAV mode and manually intervene near the final approach phase to change heading (say for example to add a little spacing or ATC vectors!), the FMC plan disappears from the EHSI as well as the FMC. I did not experience this in the 777. It is helpful when extending your approach, to rejoin it based on the visual situational awareness presented by the EHSI flight plan depiction (which also shows a white dashed line for the ILS track). So far I have have had this happen on flight plans from KSAT to KIAH, and KIAH to KSAT. Anybody else seen this?