onChange Client Script behavior differs between platform and portal after an upgrade

Before London, onChange events are fired when a field is set to the same value via a Client Script on the Service Portal. Since London, the event is not fired in this scenario, even if no script settings have been changed before/after upgrading. The onChange script behavior has changed between platform and portal after the upgrade.

1. Create a catalog item with 3 "Single Line Text" variables:
u_1, u_2 & u_3.

2. Create an onChange client script to get the value from field u_2, then put it back into the field u_2 as below:
onChange: Field = u_1:
var u2 = g_form.getValue ('u_2');
g_form.setValue ('u_2', u2);

3. Create a second script to catch onChange from the field above (u_2) and trigger a 3rd field to be updated:
onChange: Field = u_2:
var u1 = g_form.getValue('u_1');
var u2 = g_form.getValue('u_2');
var u3 = u1 + u2;
g_form.setValue('u_3',u3);

4. Open the form on the platform and notice the following expected:
Updating u_1 results in nothing happening (because u_2 is empty and the script catches newValue=='')
Updating u_2 result in an update to u_3 (appending u_1 and u_2)
Updating u_1 again triggers u_3 to change (because u_2 is not empty)

5. Try the portal and observe the following changes (in previous releases the portal used to catch the onChange event when setting a field to the same value):
Updating u_1 results in nothing happening
Updating u_2 result in an update to u_3 (appending u_1 and u_2)
Updating u_1 again does not trigger u_3 to change

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