Monoshot false triggering and latchup problem
While your schematic is incomplete (it does not show the other half of the IC), this may be the problem. CMOS MUST have all unused inputs tied to ground or Vcc. That goes for unused portions of an IC as well as unused inputs to a particular function. So ground pins 9, 10, and 11. 

While you're at it, ground 14 as well. See Figure 13 of the data sheet.