I'm sorry that I have to post this again, but somehow my previous post is not shown how I typed it in so:
[SPOILERS!]
This appeared to me to be a bug.
At first I thought the oil tank-problem was a bug too,
BUT
by now I think these "problems" are owing to the rather solemn approach of the programmers to the game.
Machinarium is weird in so many ways, and it seems, that in this game it's expected of us to solve the riddles in a straight way. For instance I got myself stuck in the room with the big oven, just in the beginning, because I screwed up the wires in a way that my robot couldn't be picked up anymore. So I had to replay this picture.
Amanita seems to have a rather strict understanding of fairness. They provide us with puzzles which are solvable only by trial and error and a bit of good observation. They even give a fair bit of hints (bulb) and solutions (play2open-handbook).
And therefore they seem to expect clean solutions.