Can't draw a line with negative coordinates ? (on Linux)

For some reason I can't draw a line with negative coordinates.

Command: li (line)
0,0
6,0
li
Command: li (line)
-2,6
Expression Syntax Error

Details:

Version: 2.2.0-alpha
Compiler: GNU GCC 8.1.1
Compiled on: Jul 23 2018
Qt Version: 5.11.3
Boost Version: 1.66.0
System: Fedora 29 (Workstation Edition)

$ uname -a
Linux Brix 4.20.6-200.fc29.x86_64 #1 SMP Thu Jan 31 15:50:43 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

I tried the same thing on Version 2.1.0 and it works fine.

This issue is discussed here:
https://github.com/LibreCAD/LibreCAD/issues/981

The solution is to use 0-1 as the formula for -1, for example.

I've submitted a fix for this issue.