The synctex command line tool distributed in TeXLive 08 is based on a buggy synctex parser. The errors are fixed in this new version, but the limitations still hold, in particular when ConTeXt is involved.
SyncTeX will synchronize with line 200 which is not very useful but not with line 100. SyncTeX has no mean to guess that line 100 will be used later on in the page. In general, the direct synchronization will give the correct page but the reverse synchronization gives a line after the correct one. In forthcoming versions, new TeX primitives will be added to catch properly this situation. This is a limitation of the original TeX engine.