I would have expected that if a file larger than the low-level input buffer size has been slurped, then the contents of multiple, consecutive read (3) calls have simply been concatenated without further ado into a single string buffer, prior to whatever processing comes next in the script. Given that the perl version and Encode version are the same, differences in cpu "native word" size and read buffer size should have no impact. (Rather, if the word/buffer size had any impact, it should affect other behaviors on slurped files, not just tr/ / /s vs. s/ +/ /g.)

So, when you compared your two machines that were both 32-bit 5.8.3 with the same version of Encode, but 32-bit vs. 64-bit cpus (smaller and larger read buffers), which one had the strange behavior with tr/ / /s going crazy?

Did the differences in Encode versions on other machines show any relation to the strange behavior? (Were you able to look at the release notes of the later Encode version(s) to see if anything relevant was fixed?)