There are 2 use-cases, in which the issue can be seen (both reproduced for ServiceNowOutput component):

1. Press "sync columns" button for FLOW (aka Main) schema for Output component. It also sync Reject schema, but is shouldn't do it for Tacokit components

2. Press "sync columns" button for Reject schema for Output component. It also sync Flow schema for the next component connected by Flow connection, but it should sync only schema of component connected by Reject flow

Actually, it is not a bug for javaject and TCOMP. Generally, Reject schema contains both columns:
1. columns from Main schema
2. additional error columns which are defined in Reject schema itself. These columns have special type: "Custom". They are shown as green, they are read-only.
The idea is following: when main schema is updated, then reject schema is updated too. Main columns of reject schema are sync with Main row.

In TaCoKit such behavior is not required.