The current implementation of HandMorph|handleMouseOver: is risky in that,
in some circumstances, it can blow up a common mistake and produce a
pollution of walkback windows that are hard to close. The side effect is due
to the use of the mouseOverTimes dictionary. The keys of this dictionary are
morphs and the values are integers representing times in milliseconds. When
the keys of the dictionary are enumerated in the fragment:

1    mouseOverTimes keys do:
2        [:m | "Check pending timers for lingering"
3        t _ mouseOverTimes at: m.
4        "and so on"

the code is assuming that m has a well defined hash. If that precondition
fails, then the morph m is in the set of keys but the invocation of at: m
produces a keyNotFound error. And of course, the error repeats again and
again.

IMO this behavior is opposite to the stability of the system for one simple
reason: the programmer who creates a Morph subclass must be aware of the
fact that each morph is going to be included in a Dictionary and thus she
must provide an infallible hash method.

Moreover, the pollution of walkbacks is not in proportion with the offending
mistake which is hard to debug and figure out. Think that most of the times,
the initialize method for a new morph has a temporary effect: once the morph
has been created, it is re-initialized to its full state. Thus a #hash that
is correct and stable from a logical point of view, can change in the
interim between steps 1 and 3 (see the fragment above).

Since Morphic is a laboratory, we should keep it safe from the accidents
produced during experimentation. Specially when this laboratory is being
visited by non-experienced users.

A partial solution to this problem is to rehash the dictionary if it fails
to access the morph:

1.    mouseOverTimes keys do:
2.        [:m | "Check pending timers for lingering"
3.        t _ mouseOverTimes at: m ifAbsent: [mouseOverTimes rehash at: m].
4.        "and so on"

This solution is partial in that it does not handle all possible defective
hashes. But I think it is safe enough. In any case, my intention is not to
provide the best solution but to rise a warning about this situation.

/Leandro

PS: I'm sending this mail to Scott since he is the author who last signed
the method in 2.5.

PPS: One more time, the MorphicWrappers made this problem apparent.