Behavior of "SORT M AS N"

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I came across a peculiar behavior of the "SORT M AS N" function.
If M contains mostly equal values, I found that the time to sort is growing rapidly.
E.g. Sorting an Array of 10000 with only 50 non zero numbers takes so long that the program seemingly stalls.
Furthermore you can not stop the sorting then. You have to stop the Smartbasic app itself !

"SORT M TO B" does not show this behavior.

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To illustrate: 2 examples

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I had hoped that Mr. K would respond....