This might explain why the changes in buffer size that I did
previously triggered problems: that way the buffer could get larger
than this threshold of 1024 bytes.  It would appear that as soon as
shrink_decoding_region is called via SHRINK_CONVERSION_REGION in
decode-coding-string, things start going haywire.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum