[NTG-context] Index register page entry numbers missing

In the following example, page number entries in the index are not displayed when a blank line is inserted in the text, but do appear without that blank. This happens with both the current 20140316 standalone beta and with TL2013. (I noticed this constructing MWEs for other index register problems. It is likely not a problem in real life, but may provide insight into other issues.) \starttext Why do the entry page numbers disappear when a blank line follows this line, and reappear when the blank line is removed? (Current beta and TL2013.) \index{AA} \placeindex \stoptext -- Rik