Change of voice within a sentence

I am currently proof-reading a technical manual and am coming across numerous instances of sentence structure which I believe to be incorrect. Here's an example:

After filling in a custom field, this will add a new field to the Add Person screen...

My problem is with the use of the word "this" after the first phrase. I re-worded to say,

After filling in a custom field, a new field will be added...

I think this is a case of active vs. passive voice. Am I right to note the first statement as incorrect grammar?

Solution 1:

"After filling in a custom field, a new field will be added..."

There are two ways I would address this.

First, if I want to stress the filling of the custom field as a cause in a cause/reaction, I would use the word, "Once," instead of the word "After."

"Once a custom field is filled, a new field will be added..."

But, I would usually rather stress the result of the cause/reaction formula.

"A new field will be added once a custom field is filled."

My reason for this is that I assume the cause, filling the custom field, is going to be done anyway, and the thing that the reader needs to be aware of is the result.