ID 365495 - Line paint tool's vertical bar to adjust the alpha is disabled when switching from other painting tools

Problem summary
The Line paint tool's vertical bar to adjust the alpha is disabled when switching from other painting tools. 

Customer reported version
modo.12.1v2

Customer reported platform
windows10

Steps to reproduce
1) Create an object to paint on.

2) Switch to the Paint tab and then select Paint Tools tab.

3) Select Airbrush paint tool. 

4) Change alpha to 20 % under FG Color. Paint on the object. 

5) Switch to Line paint tool. 

6) Alpha is still at 20 % (this reverts back to 100 % if changing to any other Paint tool again). 

7) The Line paint's tool vertical bar for alpha is disabled for adjustments.

Workaround
There is an alternative option to change alpha by typing or using a slider to adjust the value under FG color in the Line properties. 

Reproduced by support
This bug has been reproduced in:
Modo 12.1v2 - Windows 10 - CentOS 7 - MacOSX 10.13 
Modo 12.1v1 - 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 - CentOS 7 - MacOSX 10.13 

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

Expected behaviour
The vertical to adjust alpha for the Line paint tool should not be disabled. 

Actual behaviour
The vertical bar to adjust alpha for the Line paint tool is disabled.