What's wrong with this code?

[LTee]

Okay, this is driving me mad. :-D

I wrote a little routine to 'shuffle' the numbers 1 to 10 into an array, randomly. It's not exactly the best way of doing this but it was supposed to be a quick test. Regardless, it doesn't work. Or rather, it does work - the first time you run it. The second loop of the same code never completes and I can't decide if I found a bug or if I've made a mistake.

Here's the code:

Code:

dim levelMap(10) as UBYTE

randomize
for x = 1 to 10
    cls
    generateLevelMap()
    for n = 1 to 10: print levelMap(n): next n
    pause 0
next x

SUB generateLevelMap()
    dim lm as UBYTE
    dim lmPos as UBYTE = 0
    
    'clear the map first
    for lm = 1 to 10
        levelMap(n) = 0
    next lm
    
    'debug code to print the map, to make sure it's empty
    print
    for lm = 1 to 10
        print levelMap(n);",";
    next lm
    print
    pause 0
    
    'now fill it randomly
    print
    for lm = 1 to 10
        do
            'get a random position in the array
            lmPos = int(rnd * 10) + 1
            
            'debug code to print the number we randomly picked
            print lmPos;",";
            
            'debug code to print the array element if it ISN'T empty
            if levelMap(lmPos) <> 0 then
                print ink 2;levelMap(lmPos);",";
            end if
            
        loop until levelMap(lmPos) = 0
        
        'write the current number into the empty random element
        levelMap(lmPos) = lm
        
        'debug code to show that we handled this number okay
        print inverse 1;lm
        
    next lm
    
    pause 0
    cls
END SUB

I've stuck a load of debug info in there so that you can see what it's doing.

Basically it does this:
1. Clear the array to all zeroes
2. For each number, 1 to 10....
3. Look in a random array position to see if it's zero.
3a. if it isn't, loop around to 3 and try a different one
3b. if it is, write the number into that array position and move on to the next number
4. The result should be the numbers 1 to 10 in a random order in the array, after a variable number of iterations.

First run, no problem.

Second run, although the debug code shows that the array was cleared, the do...loop until loop never completes - by the time it's checking the array within that loop it contains the OLD values again, despite me having zeroed them out just a few seconds earlier.

Am I missing an obvious goof? :-D