merge_models create new outlier topic

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Hi Maarten,

I've been reducing outliers by running another topic model exclusively on them, and it has been effective. However, when attempting to merge the models, a new topic (-1) is created that doesn't exist in all models. For instance, in my initial run, I obtained 83 documents belonging to topic -1. So, I ran it again only on the topic -1 documents, resulting in the addition of two topics that covered all outlier documents, effectively eliminating outliers. However, upon merging the models using 'merge_models', I noticed a new model with topic -1 doubled in size compared to the first run, with 166 documents now belonging to topic -1. Do you have any insights into what might have caused this discrepancy?
first model:
second model on the outliers alone:
and the merge_model:
thank you!

Start by reproducing the reported workflow: fit a first topic model, fit a second model on its topic -1 documents, then run merge_models. Compare the topic assignments and outlier counts before and after merging. Done means identifying why topic -1 is duplicated or recreated and documenting or correcting the resulting behavior.

Written by the indexing model from the issue text.