The soldiers prevented Czech visitors from accessing the site. Czech authorities eventually intervened by contacting Warsaw.
The incident took place in north-eastern Moravia, in an area that forms part of the historical land of Silesia - part of which extends into today's Czech Republic.
Poland has described the incident as a mistake, although the Czech Foreign Ministry has said it has yet to receive an official explanation.
Polish soldiers had initially taken up positions on the Polish bank of the stream, but for unknown reasons had decided to make a brief incursion into Czech territory.
It is unclear how long the Polish "occupation" lasted.
The movement's local co-ordinator, Ivo Dokoupil, attempted to explain to the Poles that his group planned a brief visit to the chapel to take photographs. He was unceremoniously rebuffed.
"A soldier dressed in the uniform of a foreign state and carrying a sub-machine gun started giving me orders. It was a terrifying experience," Mr. Dokoupil told the paper.
"They wouldn't let me get closer than 10 meters."
At this point, it appears, the local Czech police force was contacted and the troops were ordered to leave.
"The placement of the border post was a result of a misunderstanding, not a deliberate act. It was corrected immediately and the case was resolved - also by the Czech side," the Polish Ministry of Defence told.
