The man page claims that Time::Local can handle dates back to 1900

It also claims to be buggy, you see that when reading on. And what you experienced is a bug, see this:

Years in the range 0..99 are interpreted as shorthand for years in the rolling "current century," defined as 50 years on either side of the current year.   ...   Whenever possible, use an absolute four digit year instead.

So however I try, 48 must be 2048 (or 148 in the counting of the   localtime()   builtin function).

Update:
Using the   "absolute four digit year instead"   works though.
Update2:
(except for dates > ~2038 ... uh!)

Cheers, Sören