Updating any product, I enter a price without decimals. (1000)
After saving the changes decimals are added in the display (1000.00)
Saving again adds the decimals to the integer part (100000.00)
Saving again adds the decimals to the integeer part again (10000000.00)
I use WP 3.5 with TwentyTwelve and Swedish language pack. In Sweden a comma is used as decimal delimiter (1000,00). Probably hence the problem.