Virgo

Looking original code in unit1.pas from git: value of P is undefined there, because it is never initialized. What happens, if you add p := nil; at the beginning of Button2Click?

Barcode scanner? Those are usually just USB keyboards. Or are Zebra ones different?

Since it is plain http you can use Wireshark to check, what is different in network request comparing browser and you program.

Right... Did not check the FMX part.

But what about TButton.DropDownMenu ? I think, that this is intended for what you are trying to achieve.

On right click it probably pops up at the location of mouse cursor... That's what it is intended to do, like all context menus.

What happens, when you rightclick on button?

Probably depends on Delphi version. In XE it grows by 1 TList<T>.Add. Or not. I did not check the content of Grow.... It doubles in size in XE. But it can still cause memory fragmentation, if reallocation has to relocate memory block.

What happens, if you add vDataList.Capacity := vMax; before filling vDataList. vDataList is using array internally, but it is constantly grown in your example. It might be the cause of those issues. Also, you really should run those test so, that one test is only one run on that execution of test program. Otherwise testing array might make use of memory that was already allocated during list testing (Delphi memory manager does not return memory to windows, when it is freed.

I guess FormatSettings.CurrencyString is not suitable, because by default returns $ for US locale?

Random EInvalidOp.... If you can use Jcl, then using Jcl8087 unit you could try adding Set8087ControlWord(Default8087CW); ClearPending8087Exceptions; before the location, where error appears. For us it helped work around about some buggy printer drivers. Also, if you happen to be using FastMM4 memory manager in FullDebugMode, then we have had random EInvalidOps with RawStackTraces on.