X cut doesn't match what's on screen

[kmun]

Describe the bug Performing an X-Cut in a raster appears to go to the next trace instead of the current one.

To Reproduce

Steps to reproduce the behavior:

1. Create a raster plot with 3 distinct traces. By default the Y axis should be numbered 0, .5, 1, 1.5, 2, 2.5, 3.
2. Verify the first trace is a rectangle starting at 0 and ending at 1 on the Y axis, and the second is from 1 to 2 and third from 2 to 3.
3. Move your mouse to below the 0.5 on the Y axis and press X to perform an X cut
4. Verify the X-Cut matches the first trace
5. Press X again to exit the X-Cut
6. Move your mouse to above the 0.5 on the Y axis and press X to perform an X cut
7. Verify the X-Cut now matches the second trace, even though the mouse was physically on the 1st trace.

Expected behavior I would think the X-Cut should match the trace under the cursor when you press the X key, it appears to round up so at 0.5 Y index it prints trace 1 and at 1.5 Y index it prints trace 2.

jsFiddle

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Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context Add any other context about the problem here.