Cursor multi-select doesn't work with Ctrl+Shift when JDT "smart caret" feature is enabled

The Eclipse multi-select feature breaks and drops back to single-cursor mode when using Ctrl+Shift with the "smart caret" feature enabled. This makes it largely useless, because I want to select either the whole variables or camel case portions at a time, not just a single character.

See here for an example video:

https://www.youtube.com/watch?v=lq-8kfnj8Ic

I am using the key bind "Multi selection down relative to anchor selection" to make my selection, placing the cursor on the right side of the variable, and then Ctrl+Shift+Left Arrow to try and select a larger portion of the variable. This drops back to single-cursor, instead of selecting across all cursors, as expected.

Start by reproducing the issue in Eclipse JDT UI with the JDT "smart caret" feature enabled, using the "Multi selection down relative to anchor selection" key binding followed by Ctrl+Shift+Left Arrow. The fix is done when selecting larger variable or camel-case portions preserves multi-cursor mode instead of returning to a single cursor.

Written by the indexing model from the issue text.