Doesn't reproduce in 7.3.1
Reproduces in 10.4.0
Repro steps:
1. Create a float/vector 1
2. set the value to 0.9
3. change the float/vector1's mode to "Integer" without making any edits to the "default" field
4. Save the graph and make a material from the graph
Expected result: the default value of the float is 0
Actual result: the default value of the float is 0.9

Alternatively, you can plug the property into a "Fraction" node (the node preview should be black, but when the bug repros, it's near-white)