find does not handle -size parameter 1 correctly

This is not a bug.

Quoting the documentation:

------------------
-size n[bckwMG]
     True if the file uses N units of space, rounding up.
[...]
The number can be prefixed with a `+' or a `-'. A plus sign
indicates that the test should succeed if the file uses at least N
units of storage (a common use of this test) and a minus sign
indicates that the test should succeed if the file uses less than
N units of storage.
------------------

Therefore -size -1k matches all empty files. Any nonempty files uses at least 1KB ("units of space,") if you you round up.

I consider this a bug, too.

The reason to not threat it as a bug might be, that you don't want a file to match -1M and +1M if it is exactly 1M, but how often do you have a file of exactly 1M? If you did a dd-command with testdata, or a split perhaps.

Status changed to 'Confirmed' because the bug affects multiple users.

OK - After a second thought, I come to the conclusion that it might be better to keep it the way it is.

Sometimes you search for files bigger than x, sometimes smaller than x and rarely exactly x, but maybe sometimes for small sizes for exactly X rounded to current measurement (4G, 4M, 4K for example).

Searching for up to 4k with -size 4k seams reasonable. Only for the size -1k it seams redundant to -empty and maybe unexpected. To have an uniform behaviour for -3k, -2k, -1k seems to be the right or at least a reasonable way.

OK - After a second thought, I come to the conclusion that it might be better to keep it the way it is. See #5 https://bugs.launchpad.net/ubuntu/+source/findutils/+bug/659771/comments/5