floors.ShowDialog();
... what is the point of using 'ShowDialog when you do nothing based on the result ?
Study this: [
^]
Put breakpoints in your code and examine the state of the varuables as you single-step through it (using F11).
Is it possible showing whatever a 'Floors is ... a Form ? ... clears the MouseButtonState ? Try capturing the MouseButtonState in a variable before you show the 'floors modally.