Cannot add more than one formula in Markdown`

Using `vim-table-mode` for markdown files, starting with the following table:

```
|---|------|
| a | 5 |
| b | 6 |
| c | 9 |
| S | 20.0 |
```

First I use `\tfa` and type in a formula: `f=Sum(1:3)`, which changes to table to the one below, as expected:

```
|---|------|
| a | 5 |
| b | 6 |
| c | 9 |
| S | 20.0 |

```

However, after adding another row and trying to add the same (or any other) formula again, something strange happens and I end up with the old formula gone, and a new one - that's not working - added:

```
|---|------|
| a | 5 |
| b | 6 |
| c | 9 |
| S | 20.0 |
| D | |
; $5,2=Sum(1:3)
```