The sloppiness here is entirely on Khandekar's part. Let's follow the chain of citations, shall we?
Fortunately, Khandekar provides an exact citation for the alleged error: the IPCC Working Group II, p. 493. Turning to that page, within section 10.6 (Case Studies), subsection 2 (The Himalayan Glaciers) we find the 2035 number:
Glaciers in the Himalaya are receding faster than in any other part of the world (see Table 10.9) and, if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high if the Earth keeps warming at the current rate. Its total area will likely shrink from the present 500,000 to 100,000 km2 by the year 2035 (WWF, 2005).
There are a couple of things to note here. First, that the IPCC report is talking specifically about Himalayan glaciers; and second, that the citation is WWF, 2005 - not Kotlyakov, 1996.
So let's look up the WWF reference, which is:
WWF (WorldWildlife Fund), 2005:An overview of glaciers, glacier retreat, and subsequent impacts in Nepal, India and China.WorldWildlife Fund, Nepal Programme, 79 pp.
Page 29 of that report says:
In 1999, a report by the Working Group on Himalayan Glaciology (WGHG) of the International Commission for Snow and Ice (ICSI) stated: “glaciers in the Himalayas are receding faster than in any other part of the world and, if the present rate continues, the livelihood [sic] of them disappearing by the year 2035 is very high”.
The trail appears to run more-or-less cold here, since I haven't been able to find the ICSI report being referenced (at least online), although it might be this one:
The above seems like a likely candidate because the author, Syed Hasnain, was quoted in numerous news stories as having said that Himalayan glaciers were likely to disappear by 2035. Although this date doesn't appear in the report, it seems likely that this is the source of the figure used in the WWF/IPCC report.
I should point out, however, that there does appear to be an error in the IPCC report - namely, the quote referring to ice area shrinking from 500,000 km^2 to 100,000 km^2 by 2035. That area could only be referring to global glacier coverage, but it appears within a section referring specifically to Himalayan glaciers. It seems that this area reference (which does appear in the Kotlyakov paper) is what Khandekar latched onto, and assumed that the date figure must also have been cribbed from the same source.
Postscript: I started this post three days ago, but I have since been beaten to the punch by a few other blogs. Drat!