Within minutes of the Czech crossing the line third in 45.47, Maslak was promoted to gold from bronze after Spain's Oscar Husillos and Luguelin Santos from the Dominican Republic were both judged to have run outside their lanes.
The decision to disqualify them was greeted with boos around the arena.
American Michael Cherry, who finished fourth in 45.84, was subsequently promoted to silver, with Trinidad's Deon Lendore, who finished fifth in 46.37, taking bronze.
A Spanish appeal against the decision was rejected after video evidence was examined. The Jury of Appeal said Husillos had been disqualified under Rule 163 governing lane infringement.
However, with images on social media appearing to also question the legitimacy of Cherry's run, the controversy seemed entirely in keeping with a championships where disqualifications have come thick and fast over two days.
The latest case left many spectators bemused and will prompt inevitable calls for a review of the rules governing running outside the lane.
"This needs to be looked at," said former world and Olympic champion Michael Johnson, who was commentating on the event for the BBC. "People just saw a race but the result did not reflect what they saw."
The spate of disqualifications had begun in heat three of the 400m on Friday when for the first time in athletics history an entire major international field was disqualified.
For a while in Saturday's final it looked as if Husillos had run the race of his life in crossing the line in 44.92, a time which would have set a championship record and shattered the European mark that has stood for 30 years.
The 24-year-old has impressed throughout the competition, improving his time in each round before running what appeared to be a well-judged final.
The celebrations were fleeting, however, and the Spanish team, like many others in these championships, were soon sifting through the rulebook for grounds to appeal.
It was probably not how Maslak, who ran his season's best, would have chosen to make history. The 27-year-old is without peer on the boards, and now has three world and three European 400m gold medals plus another gold in the 2012 outdoor European Championships, taking his overall haul to seven.
(This version of the story refiles to make clear in second paragraph Maslak was promoted to gold from bronze)
(Reporting by Neil Robinson; Editing by Clare Fallon)
Share
