[python coders] Weirdness in preview code

[Jean-Marc Lasgouttes]

In ticket #13305, in a case that spawns way too many preview 
computations, I saw evidence that many 'latex' binaries would appear in 
'top', replaced after some time by 'pdflatex'.

What is the machinery that leads to this situation? Wouldn't it be 
possible to run directly 'pdflatex'?

Sorry if I am not clear, I write here because I am not sure of what I 
should write in a ticket.

JMarc