Garbage on screen when using real VT100 on emulated PDP-11

Also posted this question in the Vintage Computer Forums. OK, I'm stumped. I'd like to use a real VT100 as a terminal with an emulated PDP-11 running RT11. When the VT100 is connected to a real PDP-11, it works fine. When connected to the emulated PDP-11, garbage characters begin to appear on the screen when, say, doing a DIR command. The garbage always starts in exactly the same place in the DIR listing. After that, garbage characters (grey squares) become interspersed with the good text. I have tried this with SIMH under Linux, connecting the VT100 to the serial console port of the Linux machine. I've also tried it under E11, using that program's built-in serial terminal capacity. Same exact error in both cases. I've looked at the RT11 SET command for TT: to see if there are any applicable parameters. Can't find any. I've set the SIMH TTO device to all its possible settings: 7B, 7P, 8B, and UC. Same stuff in all cases. I've looked at the serial settings on the VT100 to ensure 8 bits, no parity, and correct baud rate. All good. The VT100 works fine with the Linux box doing Linux-ey things. No character corruption when doing a big "ls" listing, OK with vi, etc. The SIMH and E11 emulators work fine in their virtual consoles, with no character corruption when doing a DIR, etc. Any ideas? I'd really like to, for instance, get my Raspberry Pi to be a mini PDP-11 system, but I can't get past this character garbage when using the real VT100. Help appreciated! And thanks for reading! - Earl