That does sound strange...I have never grown that flower, but I've heard they're pretty tough plants. My only guess would be to ask about watering--how much are you doing?

Dont Worry its completely normal. I have a bunch of the prurple variety and they will do this all summer until it freezes here in florida. Just a note the more water you give them the bigger they get and the faster they spread.

I put some in a clients garden last year and they did the same...they bloom pretty much for a day and then fall off...the nice thing is that they keep blooming and kept doing so into fall here in Michigan...the greenhouse I purchased them from is not growing them this year...it turned out to be one of the plants that everyone noticed and commented on...planned to double up on them this year but cannot find them.