training post validation bug

[mzouink]

one of the variables needed for gradient computation has been modified by an inplace operation: [torch.cuda.FloatTensor [72, 72, 3, 3, 3]] is at version 5035; expected version 5034 instead. Hint: enable anomaly detection to find the operation that failed to compute its gradient, with torch.autograd.set_detect_anomaly(True).