Igraph R assigning really huge (& incorrect) indegree to isolates?

Hi, I have several whole networks with a few isolates, and the networks are directed. I used the "degree, mode = “in”, loops = F) option to calculate the indegrees of each node for each network. Turns out that for all networks with vertex name = “NA” (which also didn’t send a tie, so these are isolates), a very large (much larger than the dimension of the adjacency matrix; e.g., for a network of 1000 people, the indegree is 2000+) indegree is calculated. I’m replacing the indegree attribute as 0 for them, but wondering how these numbers are calculated?

Can you show a very small but complete code example that illustrates the problem?