Starting problems

When I start the engine in my MK1 '93, it usually starts right away, and there is no running problems, it purrs like a cat. But about every third time I start the engine, it won't start, I can crank and crank, but there is absolutely no sign of life. The solution is to turn the key, and shut down the ignition, and then turn it on again, and crank the engine. Then it usually starts right away. This is no big problem for me, it's just a bit annoying. I can really not understand why this is. My only thought was that the fuel pressure was low sometimes, and when I turn the ignition off and on again, the fuel pump builds up more pressure. But this is not the case, since i've measured the pressure in all kinds of situations, and it's always fine. Anyone got an idea what it can be? Is it som software fault in the ECU, wich is corrected when I "restart" the ignition? Ideas?