Completion list appears to treat digit/underscore in identifier as a boundary

[chadunit]

Completion list invoked after a digit only searches on the characters after the digit, and upon accepting a suggestion it inserts the suggestion after the digit resulting in duplicated characters.

EDIT: Also happens with underscore.

(Note Show completion list after a character is typed is disabled, and completion list is manually summoned via Ctrl+Space.)

Expected behavior

Completion invoked on UTF8E should search for UTF8E, and entire identifier should be updated when accepting suggestion.

Actual behavior

Completion invoked on UTF8E only searches for E, and accepting the suggestion only applies it to the portion after the digit.

Related information

Visual Studio Community 2017 15.9.4
Visual F# Tools nightly 15.8.20181217.1
.NET Core SDK 2.2.101

[dsyme]

I've noticed this, there is definitely something quirky mis-interpreting identifier status. We should remove this glitch

[cartermp]

This should be addressed by #10500