WSJT-X decodes strong WSPR signal, WSPR 2.0 does not

Today I did a WSPR monitoring session on 20m. I noticed that a lot of European stations were hearing HZ1SK. I did not. Then I noticed that there was a strong signal in WSPR 2.0 on the same particular frequency that just everytime did not result in a decode. The frequency was close to the one in use by HZ1SK. Then I started WSJT-X to see if maybe this program would produce a decode. It did, and it indeed was HZ1SK, which now in WSJT-X was decoded every time. I ran both WSPR 2.0 and WSJT-X simultaneously and again WSPR 2.0 failed to decode. Why? I did notice that HZ1SK has a DT of -1.9 though. Could it be that WSJT-X is more tolerant to big DTs? On the other hand, WSPR 2.0 managed to decode several very weak signals where WSJT-X failed to. So I'm a little reluctant to make the change from WSJT 2.0 to WSJT-X for all my WSPR monitoring sessions.