DT puzzle

As you may recall, I use (very successfully) on 10m a WSPR-AXE-CW beacon by W5OLF.  In the last 6 months this has served me well.  However I was puzzled by a second report last night that both DT was way out (around 4.7) and the frequency was sometimes outside of the lower end of the WSPR sub-band. I decided to check DT locally using my FT817/PC as a receiver. Sure enough, DT was very high. Setting the clock to internet time -4 seconds made almost no difference. This evening I set my beacon TX frequency about 150Hz higher (adjusted the multi-turn pot) and, for reasons I do not understand, my DT has dropped to - 1.4 setting to internet time exactly on an even minute. It seems resetting the frequency has also fixed the DT issue. Perhaps this is something to do with Wolf's software? Anyway, I am now waiting for local Nick G4IKZ to confirm my DT findings.

UPDATE 2216z:  For reasons I do not claim to understand, I needed a long hard reset (mains power off for 20 secs) to get modulation to appear after a small frequency adjustment. All seems to be working now but the beacon will be on overnight to see if the modulation remains on.