Help with vtserver?

I am using vtserver to transfer an image of an RL02 disk (9.5 MB) to a physical pack on my PDP-11. There appear to be a few files that are corrupted in the middle of the disk. Vtserver echoes some kind of symbol to the PC console, then an "r" each time the data is actually sent to the PDP-11. In the middle of the transfer, I see on the PC display a section of 100K blocks, always from"6600K sent" to "6800K sent" that looks very strange and not like all the other sections from the beginning through 9500K with a fairly regular pattern. Vtserver starts echoing long strings of "heart" characters to the PC console, often terminated with "e" which appears to be their code for an error, and takes an extremely long time between writes to the RL02. Then the normal display and speed resumes. I usually run the serial port at 19200 but decided to try at 9600 since there is no flow control. Same result. The pack does not have bad blocks and the drive has never been a problem when running the PDP-11. I am not conversant enough in C (and definitely not with Windows file handling) to fully understand what's happening there after studying the source code... can anyone help? Thanks.