The answer is one you may not want to hear, but the fix is easy.
READ THE DATA SHEET. There is an example of using 3 HT1632s together. When using HT1632s together, only the common terminals of one of the HT1632s are connected to all of the LED arrays. The chips are operated in a slave mode, so all the multiplexing is done automatically.
The fix should be fairly simple. Just cut the traces to the common terminals on the 2nd and 3rd HT1632s, and configure them as master and slaves. The commons to have to supply enough current for all the LEDs that are on. The data sheet shows transistors to do this. Look on pages 15 & 16 of the data sheet dated 6/18/2008.