TIDA-01505: Transformer Coilcraft ZB1285-AL - problem

Part Number: TIDA-01505

Hello to all community

Does anybody use transformer Coilcraft ZB1285-AL in the design made according to TIDA-01505? I have a problem with that transformer. Verry often and without noticeable reason, insulation between primary and AUX breaks down. Coilcraft claims that the problem is transformer washing after soldering (washing solvent can damage insulation), but the transformers were not washed (this is a claim from EMS). So, I think the problem is in the insulation and transformer construction. The high voltage wire is next to +20V from AUX. When SiC turns off, the generated voltage between drain and source is 1400V (with 800V of the power supply voltage) with dV/dt around 7kV/us.

I asked Coilcraft about it but with no answer till now. 

Does anybody experience a similar problem?