The st version is faulty, some levels cannot be finished. i tested all 144 levels (actually 148 with the 'extra' levels) nd 5-6 are corrupted. Whenever it happened (bug or unplayable because of a faulty code) i had no other choice but restarting the game, and access the next lewel through the cheat-codes. This game has far too many levels anyway (though it really is enjoyable, but too much is just too much). Note that i didn't play with your version this time but i did run it to make sure and it's the same (ie missing elements or not responding the way thery are supposed to). There is one level though where your version makes a real difference: with mine, level 148th is unplayable while all plays fine with yours - But that's pretty all (i don't care about 148th cause it is just an 'extra' :D ).
On a side note, the st & amiga versions have about 15 levels which are differents compared to the others versions (go figure) but these actually are just 'reversed levels' (with the starting point located somewhere else however the levels remain exactly the same) while the others versions (even the 8 bits ones for that matter) were granted with 15 originals levels (new puzzle, levels design..). No idea why but that's plain fact. Last, the amiga version has exactly the same issue than the st one (no wonder since the levels are identicals).