Problem during adding product to quote

I have a big problem when adding product to quote. I narrowed this bug(?) to this situation and I can repeat it every time:

1. Create new organization
2. Customize quote entity to show list of related product - we want to add product using its main form (not quick create and not inline grid)
3. On customized quote form click add new product to show form like below
4. On this form fill Quantity field with any value
5. Final part - click twice on Pricing so you will get Override price and back to Use default.

In my case after I click second time on Pricing I get JavaScript error:

TypeError: Cannot read property 'errorCode' of null
at Object.<anonymous> (crodevcrm2/.../JsProvider.ashx;ids=1223231347-405283869:11181:26)
at Object.<anonymous> (crodevcrm2/.../JsProvider.ashx;ids=727017229-892652631-1552783829:1497:44)
at j (crodevcrm2/.../JsProvider.ashx;ids=727017229-892652631-1552783829:1418:29)
at Object.add [as fail] (crodevcrm2/.../JsProvider.ashx;ids=727017229-892652631-1552783829:1437:69)
at Array.<anonymous> (crodevcrm2/.../JsProvider.ashx;ids=727017229-892652631-1552783829:1495:32)
at Function.each (crodevcrm2/.../JsProvider.ashx;ids=727017229-892652631-1552783829:209:30)
at Object.<anonymous> (crodevcrm2/.../JsProvider.ashx;ids=727017229-892652631-1552783829:1492:23)
at Function.Deferred (crodevcrm2/.../JsProvider.ashx;ids=727017229-892652631-1552783829:1518:34)
at Object.then (crodevcrm2/.../JsProvider.ashx;ids=727017229-892652631-1552783829:1490:26)
at Mscrm.TurboForm.Control.FormData.refresh (crodevcrm2/.../JsProvider.ashx;ids=1223231347-405283869:11178:26)

But there is more...when I first fill all required fields like Existing product, Unit, Quantity and Price per unit and then click on Pricing record saves itself. When I change Use legacy form rendering to true in settings the error dissapears but save is still fired. There is no custom javascript here so what is the cause of this problem and how to fix this? Anyone could replicate this on his environment?

I checked this on CRM 2016 (Update 1) and CRM 365 - both on-permise, both Polish language.