Yes. According to IRFCA forum post,CEE/CR was quoted saying that CR had tried out this arrangement on a trial basis. But the reasons,though don't make much sense have been given for this. It is that HHP locos are only needed for the arrangement(WAP-7/WDP-4D) which may not be available all the time. False. The train runs with HHP locos all the time as LHP locos can't haul 25 coaches at that stretch on the plateau region. So HHP is needed whatsoever is the case. Second is that time loss was happening. This again is false as time is never kept up in this single line stretch from WADI to Jinti Road(double line begins at WADI for down and at Jinti Road for up). Jinti road is around 15 minutes towards Solapur from DD. Bhigwan to New Delhi is fully double electric line where the train goes at good speed. The actual reason...
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is still unknown. Fuel consumption? Loco strain for the diesel?

The reasons were not entirely senseless.
1) The arrangement was not saving time - This is true to some extent. Even with the piggy-backing arrangement, the d-loco still has to be shunted around, and needs to be stabled in another line. Even when the LC option was tried out initially, CR mentioned that Wadi had some constraints in stabling locos. The same constraints will still hold. But yes, only one loco has to be shunted, instead of 2, so some time can be saved.
2) Time loss on sections (tied with the first...
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reason as well) - WDP4D is really insufficient for KK's load now. Even though it is called a HHP loco, it is still only 4500HP, lesser power than a WAP4, which itself runs almost at the limit with a 26 coach ICF rake. Now, KK's regular link till DD is a WAP7, which at 123 tons, weights almost as much as a 3 ICF coaches. Add this to KK's 25 coach rake and the 4500HP WDP4D has to effectively haul a 28 coach rake. The balancing speed of the train will also drop with the added weight.
Maintaining the schedule is different from not being able to maintain time on a section. With the insufficient loco power hauling it, now it will take longer to clear sections, which will indirectly lead to more delays as controllers will be forced to delay the struggling train to give way for other trains. It will add on to the delays being caused by the controllers and force them to delay it even more.
The 25 coach rake of KK really kills the deal for this kind of arrangement. A single EMD is grossly under-powered for this job.
Also, some stations on the route do not have loop lines long enough for 24 coach rakes. With the 25 coach rake and the 2 locos at the head, crossings at Pophlaj are a strict no-no for KK now and it will definitely get delayed even more.
Bottom-line is that a DUW run looks like the best option for the foreseeable future. Or SCR can take over the diesel links and arrange a loco change at Guntakal.