On Sunday, August 11, 2019 at 9:09:23 PM UTC-5, Chalo wrote:
Note that Shimano road and MTB 10 speed derailleurs have different pull ratios. Rear derailleurs and shifters are miscible up to 9 speed.

On my touring bike I am using 10 speed Shimano 105 STI levers and Shimano Deore 9 speed rear derailleur. Shifts good. 44-33-20 chainrings, 11-32 ten speed cassette. I think with Shimano Road 10 speed, it works with road 10 rear derailleurs, and mountain 9 rear derailleurs. But no 10 road STI and 10 mountain rear derailleur. No no.

On this malfunctioning cyclo cross bike I am going read 10 speed Shimano STI levers and Shimano 105 ten speed medium cage rear derailleur. So no potential for incompatibility.