Thanks for the detailed investiations and report. Finally I could reproduce the problem by having messages with a text body size close to 250000 bytes (some internal limit). Never thought that someone really has the patience to write 250'000 chars in a single message, but I guess you did some copy/paste from a large file. Thought in such cases people use attachments. Nevertheless, I fixed an internal memory allocation problem, now it shoudl be fine to have such large messages. Change is committed.
I cut the log in two parts w/o modifying the content and the search runs. It seems that the size of this entrie 426 is closed to a limit (as during testing, i met a message after clicking save to recompile elog to increase a size of something), so it could be the problem.
I reduced the entrie size by extracting the last part in a new entrie and it seems to be OK.
The old size was 250099 bytes. New size is 240084.
I hope this will be OK.