An A320 FMGC dropped an arrival intersection altitude constraint and so the aircraft continued its descent to the point where the EGPWS issued a TERRAIN warning. During the go around a FWC failure caused incorrect flap position and speed alerts but neither the FWC failure nor flap exceedences were recorded in the automated post flight maintenance log.

Narrative

We were cleared for the Localizer 27 approach. First Officer was pilot flying. ATC issued usual speed restrictions and we briefed about that and the Aircraft ahead of us. Specifically [we were] to maintain 210 KTS to the first intersection then 170 to the second intersection. Descending from 3;600 FT from the third to the fourth intersection I noticed an unusually high sink rate. Looking at the flight plan page I noticed the constraint for the fourth intersection i.e.; 2;400 FT; had dropped out of the box. The First Officer had a managed descent selected and the altitude selected in the altitude box was 1;800 for the restriction at the second intersection. I pointed out the conflicting info and the First Officer had already begun to make corrections. Due to a higher descent rate the aircraft did not level off immediately and simultaneously I believe due to the sink rate a terrain GPWS was triggered. I called missed approach and the First Officer performed a climbing maneuver commensurate with the GPWS warning. Another factor with this scenario is that we had a FWC failure during the flight that was giving other warnings that were not correct involving flap positions and speeds. In other words a great deal was happening at once during our go around. Priority was given to GPWS warning which was 'Terrain'. The procedures were followed correctly and we notified ATC we were going around. The following approach and landing was uneventful. After arriving at the gate I discussed at length with the Maintenance personnel what indications we were getting and they could not find any evidence of speed exceedances or control surface position. Although we had warnings generated perhaps by the faulty Flight Warning Computer (FWC)? I believe we generated a Terrain GPWS warning due to a sink rate issue. Regardless of the cause the necessary steps and actions were taken to maintain the safety of the aircraft. In this case a go around with priority for a terrain warning. Nothing occurred out of the ordinary other than a constraint issue on a non-precision approach. The deviation was identified and the proper action initiated. The additional factors with a failed FWC were a surprise. But flying the airplane was the priority. Perhaps a little more info related to such a system failure may be useful. Information provided by the QRH and subsequent equipment manuals are adequate for basic knowledge. I would have like to have known that there may be spurious warnings triggered for flight configurations. If in fact they do? Or maybe [it was] just a coincidence.