It appears from your second image that you have inadvertently added a column. Note the skinny cell at far right of the red row.

Word tables can be tricky. One aspect that keeps them from behaving is columns not aligning perfectly. If one row's cells are not aligned perfectly with the rows above and below, for example, a column selection may annoyingly select a different cell than expected in that row, and throw the selection off below it as well. Fixing alignment sometimes requires increasing the magnification enough to see a discrepancy which screen resolution prevents recognizing at lower magnifications.

Similarly, merged or split cells can confuse Word when it comes to pasting. Word wants it all to line up just so, with no surprises, such as receiving (i.e., having pasted in) a row with more or fewer cells than the rows immediately adjacent.

I hope this will help you solve your difficulty.

Best,
Ulodesk