Link232 Wifimodem issues continue

Sorry to bother you again with Wi-Fi modem questions.
Even though the major issues have been resolved, I’d like to look into this flow control problem as well.

Description of the issue:
The screen output breaks up, as if flow control weren't active. I’ve tried various ways to verify that it is enabled, yet the problem persists—specifically on the PC and the Amiga.

I’ve had a bit of extra time to look into the matter again.
I noticed something odd:
the text/menus break apart when the C64 shifts the screen upwards,
and then return to normal once the screen shift stops?!?
How are these things connected?

This happens even when I use the Amiga as a terminal; 
although the text appears on the screen at a speed of around 300 baud, 
the C64's screen scrolling still messes up the output.

Another question: 
which flow control pin does the machine-language program monitor 
when the BBS is sending data? I need to know this so I can verify that 
the modem is actually working correctly. 
There are no flow control issues when using C64 terminals, though...?!?