it's been years since I read anything other then that NSFW 4chan write up picture, so if you have a picture of text saying that kenders do learn over time about personal property I will admit I am wrong...
But they understand personal property. They just deal with it differently than most. Having just the one book in front of me at the moment, I can't provide an example of them learning not to borrow, but there are references to them learning to temper some of their other natures:
Some kender might allow their curiosity to
overcome their common sense when facing
unusual opponents, such as dragons, though
they eventually learn to run when running is
best.
A kender's fellow adventurers often have to
teach him that certain things have big. nasty
teeth and that avoiding these things is often in
the kender's best interests, regardless of what
the kender's opinions are in the matter.
Whenever a kender displays an inordinately
sensible attitude about danger, it is probably
because the kender realizes that continued
curiosity will ruin any further chances of doing
exciting things ever again.
A later section mentions some information about their sense of property:
On the other hand, kender, like everyone
else, do not like the idea of someone deliber-
ately taking an item from someone else with-
out the latter's permission. To be called a thief
is still considered a base insult. This assertion
sounds remarkable in view of the fact that
kender constantly borrow things from each
other and from visitors (without asking) in
their communities. Kender don't regard their
idea of borrowing as stealing, however. If they
need something, they'll take it. If they see
something interesting, they'll pick it up and
pocket it. A popular proverb defines a kender
heirloom as anything that remains for more
than three weeks inside a kender's home.
There are some other sections that give the impression that Kender are so carefree as to seem irresponsible, but when it comes to something important, they manage to get things done. So I imagine the blacksmith's hammers would be found. It would probably become something of a game for Kender to constantly reclaim and replace various items around town as they are needed. I like to think of them as chaotic in the extreme, but in a way that simply works.