Some questions about common emitter NPN transistor when the base is open
Transistor models are simplifications. Do not assume extreme reliability in cases where transistors are used abnormally. Open base is abnormal. 

Think about an internal resistor between C and B. It makes your base connected. That resistor probably


is not specified in datasheets
depends on temperature
doesn't obey ohms law


The datasheets often give an external resistor to be inserted between B and E which is small enough to sink the otherwise undocumented CB leakage to non-harmful.