Records with no skills disappear in multi-grouping demo

[bmblb]

There are several scenarios leading to disappearing record.

1. On a grouped store edit any record and remove all skills. See there is no group with empty skills.
2. Stop grouping. You will see no record with empty skills anyway
3. On an ungrouped store clear skills from another record. See record stays in view.
4. Group store by skill. See there is no group with empty skills
5. Ungroup, see record is not visible anymore

If you check record count on steps 3 and 5, you will see one record is missing.

Interesting part is that records seemingly get removed missing the removed cache on a store. Meaning nobody would be aware of the record missing. i.e. store.count decreases, but store.removed keeps having just one value (or none)