minor Oop spoiler - GoF plothole?

[Brooks]

No: HPFGUIDX 62870

When Dobby levitates the pudding in CoS, and when Harry summons his 
Patronus in OoP, one of the charges against him is that he violated 
the International Secrecy Act by performing magic in front of 
Muggles. So what, if anything, happened to Arthur Weasley after he 
temporarily hooked the Dursley's house into the Floo network in GoF?

Furthermore it seems there is no exception to the Secrecy Act when 
the Muggles in question already know all about the existence of the 
Wizarding community, a situation which I find odd, since there are so 
many Muggles that DO know. (Did someone run up and down Diagon Alley 
yelling "No Magic. Muggles in the area." when the Drs. Granger 
arrived in CoS?)