ID 378039 - Using the Arc tool to snap the angle at 180 degrees with Snapping function enabled, collapses the arc into a line

​Problem summary
Using the Arc tool to snap the angle at 180 degrees with Snapping function enabled, collapses the arc into a line instead of drawing a half circle. If the angle is left at 180 degrees when reactivating the tool, the arc is drawn as a half circle. 

Alternatively, if the "Angle" value is only set to 0 degrees in the Tool Properties, the arc also collapses into a line and still remains as a single line when changing the value up to and back from 180 degrees by the Tool Properties. 

Customer reported version
Modo 12.2v1 

Customer reported platform
MacOSX 10.14

Steps to reproduce

Alternative 1: 

1) Open Modo.

2) In the 3D Viewport, change the view to "Top".

3) Go to Geometry -> Primitive Tools and then activate the "Arc Tool". 

4) In the Tool Properties of the "Arc Tool", activate Snapping with "Grid" enabled.

5) Draw the arc and then grab the angle handle to snap the angle of the arc to 180 degrees. 

6) The arc is now collapsed into a line of 0 degrees, which is incorrect and should be a half circle at 180 degrees. The text that displays the current angle in the viewport is not at the correct location. The text is instead displayed at the origin of the arc where the "Radius" value is displayed. 

Alternative 2: 

1) Open Modo and change the view to "Top". 

2) Activate the "Arc Tool" in Geometry -> Primitive Tools. 

3) Open the Tool Properties and change the "Angle" value to 0 degrees. If starting only from 0 degrees, the arc collapses into a line and still remains as a single line when changing the "Angle" value up to and back from 180 degrees by the Tool Properties. 

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Workaround

• Grab the angle handle while holding down "Ctrl" to change the angle to 180 degrees. 
  

• Disable the tool and enable it when the angle is left at 180 degrees. If you now draw the arc, it is drawn as a half circle and the "Angle" value is displayed at the correct location of the viewport. 

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Reproduced by support

This bug has been reproduced in:
Modo 12.2v1 - Windows 10 - MacOSX 10.13 - CentOS 7 

Modo 12.1v2 - Windows 10 

Modo 12.0v1 - Windows 10 

Modo 11.2v3 - Windows 10 

Modo 11.1v1 - Windows 10 

Modo 11.0v3 - Windows 10 

Modo 10.2v4 - Windows 10 - MacOSX 10.13 - CentOS 7 

Earliest version tested

Modo 10.2v4 - This issue appears to be in all versions of the product.

Expected behaviour
The Arc tool should draw an arc that is a half circle when using the Snapping function to snap the angle at 180 degrees. 

Actual behaviour
The arc is collapsed into a single line of 0 degrees if the angle is snapped at 180 degrees with the Snapping function.