Maximum number of literal values for SetDelayed?

Question

Under what circumstances should I expect Mathematica to turn a delayed assignment into an immediate assignment? I have put together a minimal example (available here) which demonstrates this behavior. There is a package which contains basically the following, where each line has its own cell in the notebook from which the package is generated:

setMyVar[a] := (var = 1;)
setMyVar[b] := (var = 2;)
setMyVar[c] := (var = 3;)
setMyVar[d] := (var = 4;)
setMyVar[e] := (var = 5;)
setMyVar[f] := (var = 6;)
setMyVar[g] := (var = 7;)
setMyVar[h] := (var = 8;)
setMyVar[i] := (var = 9;)
setMyVar[j] := (var = 10;)
setMyVar[k] := (var = 11;)
setMyVar[l] := (var = 12;)
setMyVar[m] := (var = 13;)
setMyVar[n] := (var = 14;)
setMyVar[o] := (var = 15;)
setMyVar[p] := (var = 16;)
setMyVar[q] := (var = 17;)
setMyVar[r] := (var = 18;)
setMyVar[s] := (var = 19;)
setMyVar[t] := (var = 20;)

When I load this package and then evaluate Definition[setMyVar] every assignment is defined as a Set rather than a SetDelayed in Mathematica 9.0.0.0. However if I comment out any three of these, everything returns to being SetDelayed. Does anyone have any idea why Mathematica would do this? If so, is there a system variable I can change to address this problem? The tarball also contains a notebook which demonstrates the behavior in a setting which is not loaded from a package.

This does not come up if everything is in a single cell, but arranging everything in such a way is not practical for the actual application in which I ran across this. To address why this might be considered to be a problem, I ran across this while using DistributeDefinitions["Context"] which as stated in the documentation essentially runs ParallelEvaluate on every statement in the context, and this is causing things to be evaluated which should not be.

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Edit to add: I have confirmed that this occurs with Mathematica 9.0.1.0 as well. Both machines tested are Linux x86-64.

Answer 1

If you test the code above, i.e. run

mySetVar[t]

it works correctly (i.e. var is set to 20).

The problem is actually one of "Definition" rather than SetDelayed. Definition is a weird function that simply prints some info to the screen. In this case, it gets it wrong, i.e. there is a bug in Definition. As a work around, if you want authoritative information on a symbol, use

DownValues[mySetVar]