You're confusing ghosting with SCR latch drop induced flickering.

On old Bally's/Classic Stern, the incandescent lamps drew enough amperage to keep the controlling transistor (SCR) latched on (It's 250ma for #44/#555, 150ma for #47). Once you put in a LED, they consume significantly less amperage, in the 10ma to 40ma range depending. Therefore the SCR drops the sink causing the LED to go out, only to have the CPU tell it to turn back on on the next refresh cycle causing the LED to turn back on. Depending on when the drop occurs and refresh, it make it seem like a random flicker.

Ghosting, on the other hand is when a lamp matrix is used (Bally/Classic stern do NOT use a matrix--they have a separate wire going to every controlled lamp where matrixes share the same wires across up to 8 lamps) Ghosting appears as a dimly lit LED due to the pulse frequency of the voltage on the matrix.

This fix to keep the SCR's latched has been known for a long time. There is another thread here the discusses the various resistor values tried and alternate ways to fix this problem:

http://pinside.com/pinball/forum/topic/led-lights-in-bally-1978-ss-game-new-board-required

Basically any game that uses a matrix -- E.g. Besides classic Bally/Stern, most everything else. Some newer ones can have software based fixes. Older ones simply require blocking capacitors (non ghosting) LEDs; or you deal with it.

Both of my System11 games exhibit ghosting -- though it's minor enough that I can live with the low amount, and infrequent times it occurs and stick with 30c LEDs instead of $1.50 ones in different styles/brightnesses as well. Other games it is so bad that people must convert to non-ghosting LEDs, upgrade firmware or try other techniques.