Linking to a subpage /like this or /like this puts the page in Main
due to the preceeding whitespace.
Yes, this is extremely bad style, but the software should be smarter than to
create a non-subpage potentially in the wrong namespace when newbies are likely
to make this error.
In fact, I can see no good reason at all for NOT trimming pre and post
whitespace from poorly formed wikilinks like this, unless the style is
considered so bad that the links should simply not work at all. In either case,
the current non-trimming system is a bad idea.