=   =
| | | |
 =   =
| | | |
 =   =
 1   2

Assuming common anode 7-segments.
"1" is displayed on 1. 7-segment, "2" is displayed on 2. 7-segment, the there is a delay (e.g. other 7-segments follow and all are off).

When high-side driver for 1. 7-segment is turned off, it remains on for a while; and when the low drivers start driving the "2", a faint "2" appears on the 1. 7-segment (in fact, the segment common for "1" and "2" is even brighter than the bright ones, but one cannot notice that).
This is of course the same for multiplexing dot matrices; you might see a faint ghost of the following row on the previous row (assuming rows are driven high, columns low).

Of course, the severity of this effect depends on the power PNP type, construction, method of driving it etc. etc.

Jan Waclawek