(vbs) Autorefresh of Javascript form refresh after data entry

I'm attempting to auto-fill out a web form via vbs. I can fill out the form fine, but when my script fills it out vs when I manually fill it out produces a different reaction from the form. The form is supposed to calculate BMI based on my entry and ENABLE the save button, however, it only does this if I enter this data manually. I need to trigger whatever function is causing this check for entry. The problem is, I'm not finding any clues as to which function is doing this...

Here is the script I used to fill out the field:

IE.Document.getElementsByTagName("input")("txtWeight").value = "170"
Do Until IE.ReadyState = 4: WScript.sleep 15: Loop

Here are examples of the form and element in both states when weight filled out programmatically and manually. Notice save button in element disabled and BMI not calculated:

PROGRAMMATICALLY

Here is an example with it manually filled out calculating BMI and save button enabled (element not showing "disabled"):

MANUALLY

Here is complete HTML pastebin: http://ift.tt/1EQPCBf

I realize this may not be much to go on. May be tough to get help on this since getting to this point on the site requires a login. If this requires any info I didn't provide, let me know and I'll grab it. Thanks!