An unidentified HEO object

Yesterday evening was very clear. I photographed the STSS Demo r/b (09-052C) using the EF 50/2.5 Macro, and then switched to the EF 100/2.8 Macro USM to capture the HEO objects USA 184 (06-027A) and USA 198 (07-060A).

One of the four images capturing the latter, contained an unknown object some 3 degrees south of USA 198. It is a clear trail, similar to that of USA 198 in length and direction. It shows evidence of being the capture of a brief flare. And it doesn't match any known object from the unclassified or classified catalogues.

Below is a detail of the image showing the object (the inset is a 200% blow-up). The trail is about 20 pixels long, or about 3.5'.

click image to enlarge