Imputation Doesn't Work on Some Sparse Data Sets

[nikicc]

Orange version

3.5.0.dev0+554b885

Expected behavior

Imputation fills missing values.

Actual behavior

It doesn't fill missing values on some data sets.

Steps to reproduce the behavior

Most easily reproducible on Text. Load Election-2016 tweets, pass them through BoW and Impute with Average. The resulting matrix still has some missing values.

Additional info (worksheets, data, screenshots, ...)