can_read ( [ TIMEOUT ] )
           Return an array of handles that are ready for reading. "TIM
+EOUT" is
           the maximum amount of time to wait before returning an empt
+y list, in
           seconds, possibly fractional. If "TIMEOUT" is not given and
+ any han-
           dles are registered then the call will block.
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It never says it's always going to wait for the TIMEOUT, it just says it's not going to wait longer than the timeout.

AFAIK this might be a bug in perl, a bug in your OS, or it might be a completely reasonable effect of the way select() is implemented... According to my select(2) manpage (on Linux) errno should be set when select(2) returns -1. Try printing $! in your else routine.

Also note that you should not use buffered IO when using select (so use sysread() and syswrite() instead of read() if you don't already).