Electrolytic capacitor placed with the wrong polarity

[Trozze]

After recapping a dead CRT monitor chassis board with over 50 caps (Yes I checked several times but missed it  ) I managed to put one cap the wrong way around  and it vented, so I replaced it.
The CRT is now up and running, however it has some small horizontal interference/ghosting on some bright parts of the image... Might be the tube, maybe something broke when the cap vent on backwards.

This made me thinking.. we all know what happens when you put a cap backwards - it vents or explodes, but what happens to the circuit during and after this? 

It’s a cap for smoothing the 12v line, when and after a cap fail this way, does it short circuit, acts like a resistor, still works somewhat but with out of spec?

[Zero999]

Firstly the capacitor will present a short circuit to the circuit, then after all the electrolyte has boiled off and it's vented, it will go open circuit again, with a capacitance much smaller than the rated value.